Gostaríamos de agradecer a Andrew Cripps e unidade BioResource na Universidade de Reading. Esta pesquisa foi financiada pelo BBSRC (número de concessão: BB/K010123/1). Dados associados a este trabalho são livremente disponíveis a partir do Y.Z. (ying.zheng@reading.ac.uk).

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A., Koch, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+origin+of+extracellular+fields+and+currents+—+EEG,+ECoG,+LFP+and+spikes.">The origin of extracellular fields and currents — EEG, ECoG, LFP and spikes.</a> Nat Rev Neurosci. 13 (6), 407-420 (2012).</li><li>Einevoll, G. T., Kayser, C., Logothetis, N. 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X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Where+Does+EEG+Come+From+and+What+Does+It+Mean?.">Where Does EEG Come From and What Does It Mean?.</a> Trends Neurosci. 40 (4), 208-218 (2017).</li><li>Bojak, I., Oostendorp, T., Reid, A., K&#246;tter, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Connecting+Mean+Field+Models+of+Neural+Activity+to+EEG+and+fMRI+Data.">Connecting Mean Field Models of Neural Activity to EEG and fMRI Data.</a> Brain Topogr. 23 (2), 139-149 (2010).</li><li>Coombes, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large-scale+neural+dynamics:+Simple+and+complex.">Large-scale neural dynamics: Simple and complex.</a> Neuroimage. 52 (3), 731-739 (2010).</li><li>Deco, G., Jirsa, V. K., Robinson, P. A., Breakspear, M., Friston, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+dynamic+brain:+from+spiking+neurons+to+neural-masses+and+cortical+fields.">The dynamic brain: from spiking neurons to neural-masses and cortical fields.</a> PLoS Comput. Biol. 4 (8), e1000092 (2008).</li><li>Pinotsis, D. A., Friston, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+fields,+spectral+responses+and+lateral+connections.">Neural fields, spectral responses and lateral connections.</a> Neuroimage. 55 (1), 39-48 (2011).</li><li>Riera, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pitfalls+in+the+dipolar+model+for+the+neocortical+EEG+sources.">Pitfalls in the dipolar model for the neocortical EEG sources.</a> J Neurophysiol. 108 (4), 956-975 (2012).</li><li>Valdes, P. A., Jimenez, J. C., Riera, J., Biscay, R., Ozaki, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonlinear+EEG+analysis+based+on+a+neural+mass+model.">Nonlinear EEG analysis based on a neural mass model.</a> Biol Cybern. 81 (5), 415-424 (1999).</li><li>Musall, S., von Pf&#246;stl, V., Rauch, A., Logothetis, N. K., Whittingstall, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+Neural+Synchrony+on+Surface+EEG.">Effects of Neural Synchrony on Surface EEG.</a> Cereb Cortex. 24 (4), 1045-1053 (2014).</li><li>Snyder, A. C., Morais, M. J., Willis, C. M., Smith, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Global+network+influences+on+local+functional+connectivity.">Global network influences on local functional connectivity.</a> Nat Neurosci. 18 (5), 736-743 (2015).</li><li>Mayhew, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectroscopic+analysis+of+neural+activity+in+brain:+Increased+oxygen+consumption+following+activation+of+barrel+cortex.">Spectroscopic analysis of neural activity in brain: Increased oxygen consumption following activation of barrel cortex.</a> Neuroimage. 12 (6), 664-675 (2000).</li><li>Paxinos, G., Watson, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Rat Brain in Stereotaxic Coordinates. , (2005).</li><li>Martindale, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+hemodynamic+impulse+response+to+a+single+neural+event.">The hemodynamic impulse response to a single neural event.</a> J Cereb Blood Flow Metab. 23 (5), 546-555 (2003).</li><li>Pettersen, K. H., Devor, A., Ulbert, I., Dale, A. M., Einevoll, G. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current-source+density+estimation+based+on+inversion+of+electrostatic+forward+solution:+Effects+of+finite+extent+of+neuronal+activity+and+conductivity+discontinuities.">Current-source density estimation based on inversion of electrostatic forward solution: Effects of finite extent of neuronal activity and conductivity discontinuities.</a> J Neurosci Methods. 154 (1-2), 116-133 (2006).</li><li>Thomson, D. J., et al., Fitzgerald, W. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multitaper+analysis+of+nonstationary+and+nonlinear+time+series+data.">Multitaper analysis of nonstationary and nonlinear time series data.</a> Nonlinear and Nonstationary Signal Processing. , 317-394 (2000).</li><li>Bae, J., Deshmukh, A., Song, Y., Riera, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brain+Source+Imaging+in+Preclinical+Rat+Models+of+Focal+Epilepsy+using+High-Resolution+EEG+Recordings.">Brain Source Imaging in Preclinical Rat Models of Focal Epilepsy using High-Resolution EEG Recordings.</a> Journal of Visualized Experiments : JoVE. (100), e52700 (2015).</li><li>Baumann, S. B., Wozny, D. R., Kelly, S. K., Meno, F. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+electrical+conductivity+of+human+cerebrospinal+fluid+at+body+temperature.">The electrical conductivity of human cerebrospinal fluid at body temperature.</a> IEEE Trans Biomed Eng. 44 (3), 220-223 (1997).</li><li>Wendel, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Influence+of+Age+and+Skull+Conductivity+on+Surface+and+Subdermal+Bipolar+EEG+Leads.">The Influence of Age and Skull Conductivity on Surface and Subdermal Bipolar EEG Leads.</a> Computational Intelligence and Neuroscience. 2010, (2010).</li><li>Flemming, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+the+distortion+of+EEG+signals+caused+by+a+hole+in+the+skull+mimicking+the+fontanel+in+the+skull+of+human+neonates.">Evaluation of the distortion of EEG signals caused by a hole in the skull mimicking the fontanel in the skull of human neonates.</a> Clin Neurophysiol. 116 (5), 1141-1152 (2005).</li></ol>

Os autores não têm nada para divulgar.

Descrevemos um procedimento experimental para gravação simultânea de sinais de EEG e LFP co localizadas de um rato de isoflurano anestesiados em resposta à estimulação de almofada whisker. Um microeléctrodo foi inserido o neocórtex através de uma abertura no eletrodo de aranha EEG que foi alinhado com um orifício de trépano, perfurado o crânio. O eletrodo foi fixado ao crânio por um condutor e adesivo EEG colar23. O cone de nariz, usado para a administração de isoflurano foi modificado para que os eletrodos de estimulação pode ser inserido a almofada dos whiskers com facilidade.
O colar de EEG foi eficaz na montagem do eletrodo de aranha firmemente ao crânio, proporcionando excelente condutividade elétrica durante todo o dia experimental, sem a necessidade de aplicativos adicionais de colar. Substituiu o uso indesejável de colagem para reparar a periferia do eléctrodo aranha no crânio, como colagem é não-condutora e pode aumentar a impedância do eléctrodo se corre entre o crânio e o eletrodo. Colar de EEG tem um número de vantagens sobre gel de EEG, que é difícil de forma ao redor do orifício de trépano e pode secar durante o experimento, resultando em sinais de EEG pobres.
Como o rato foi colocado dentro de uma gaiola de Faraday, ruído elétrico devido ao ambiente extremamente foi atenuado. No entanto, às vezes o sinal neural ainda era muito barulhento. Na maioria dos casos, isso foi causado pelo eletrodo de referência não está bem posicionado e, portanto, precisava ser reajustado ou EEG mais colar usado. Outro problema comum que era a LFP evocado pequena amplitude. Isto pode ser devido o microeléctrodo não posicionado no centro da região cortical ativada pelos eletrodos de estimulação. Em vez de re-inserir o microeléctrodo, que poderia causar mais danos para os neurônios locais, geralmente ajustamos a posição dos eléctrodos de estimulação da almofada da Suiça até uma razoável amplitude de LFP (> 3 mV) podia ser observada.
Uma das limitações da técnica é a resolução espacial pobre do eléctrodo aranha, que tem um diâmetro de 6 mm. Isto é grande em comparação com o tamanho do crânio de ratos. Infelizmente, o eletrodo de aranha usado aqui é o menor disponível para compra. Será desejável para reduzir o diâmetro do eletrodo aranha para 2-4 mm, aumentando assim a especificidade espacial de gravações de EEG, fazendo a comparação entre o sinal de EEG e o supragranular LFP sinal menos ambíguo.
Vários passos críticos no protocolo precisam de atenção especial. O primeiro é a inserção do microeléctrodo através do orifício de trépano. Como a dura-máter, caso contrário está intacta, a precisão da inserção é crucial. Uma leve resistência na ponta do eletrodo geralmente significa que o eletrodo não está posicionado corretamente. Ele deve ser aumentado, posição ajustada e re-inserido. O segundo é a posição do cone de nariz no rato. Não deve ser demasiado solta, como o isoflurano pode escapar através do cone. Também não deve ser muito apertado, pois isso pode obstruir as narinas do rato e causar dificuldade para respirar. Atenção especial também é necessário para garantir que a amplitude da gravação do EEG é muito menor (geralmente 5 a 10 vezes menor) do que a LFP top canais de gravação. Se eles são semelhantes, é uma indicação de que a sonda de EEG tem entrar em contato direto ou indireto com o microeléctrodo. Um contato indireto é geralmente através do fluido espinal cerebral (CSF) que às vezes enche o buraco perfurado no crânio. A condutividade do CSF é tipicamente 100 vezes do crânio24,25. Assim, se o nível do CSF do orifício de trépano é suficientemente elevado, pode fazer contato com o eletrodo de aranha. Para evitar isso, o furo deve ser limpos frequentemente com esponjas algodão super absorvente, tais como as lanças de absorção.
O efeito de uma trepanação (diâmetro < 2 mm) no crânio no EEG gravação em torno do buraco foi estudada, colocando outro eletrodo de aranha no crânio intacto no topo do barril ipsi-lateral córtex para que as gravações de EEG bilaterais podem ser comparadas. Os resultados mostrados na Figura 9 e Figura 10, sugiro que o efeito de ser insignificante para o nível de significância de 0,05. Outros fatores que afetam a amplitude do EEG incluem quão bem o colar de EEG foi em contato com o crânio, firme como o eletrodo foi pressionado para o colar e a extensão espacial da pasta de EEG no crânio.
Também vale a pena notar que o protocolo descrito aqui registada crânio EEG, que é diferente do couro cabeludo EEG usado em estudos humanos de EEG. O couro cabeludo age como um resistor ou um filtro low-pass, que irá reduzir a relação sinal-ruído de EEG gravação ainda mais.
Finalmente, comparação da dinâmica temporal do ERP e da LFP evocado em camadas corticais sugerem que o potencial evocado somatossensorial reflete melhor a LFP na camada supragranular do córtex do que na granular e camadas de infragranular. Isto está de acordo com nossos anteriores trabalhos6, demonstrando que o segmento inicial (P1) do ERP está relacionado com o atual retorno decorrente da afluência do excitatórios sináptica atual que ocorrem na camada granular, enquanto a subsequente diminuição ( N1) em ERP pode estar relacionado com a chegada atrasada de camadas aferente a cortical talâmica II/III e/ou feedforward sinais de camadas corticais mais profundas. Em conclusão, gravações simultâneas de EEG/LFP podem aumentar a compreensão do genesis neural de EEG e facilitar a modelagem matemática de EEG em termos de sinais neurais em camadas corticais.

É geralmente aceite que LFPs gravadas através de microeletrodos principalmente refletem a soma ponderada das atividades sinápticas excitatórias e inibitórias sincronizadas de populações locais de neural piramidal1,2,3 , 4. nossa pesquisa recente demonstrou que o perfil do sinal do LFP pode ser separado em componentes de excitação e inibição de5,6. No entanto, LFP é normalmente medido através de um procedimento invasivo, não é adequado para a maioria dos estudos do cérebro humano.
Por outro lado, o EEG é uma técnica não-invasiva para medir a atividade elétrica do cérebro. É amplamente utilizado como uma ferramenta diagnóstica para certos tipos de doenças neurológicas como a epilepsia e como uma ferramenta de pesquisa em estudos cognitivos humanos. Apesar de sua popularidade, uma grande limitação de EEG é a incapacidade de interpretar seus perfis temporais precisamente em termos do subjacente sinais neurais7,8,9.
Cada vez mais, os modelos matemáticos de EEG são desenvolvidos para melhorar a compreensão do cérebro função10,11,12,13,14,15. A maioria dos modelos existentes de EEG é desenvolvida com base na frequência domínio as características do modelo previsto de saída para o espectro de dados de EEG durante a atividade espontânea de montagem, e muito poucos modelos de EEG podem gerar potenciais evocados sensoriais realistas. Neste contexto, gravações simultâneas de EEG e LFP irão fornecer uma visão importante e restrições para o desenvolvimento de modelos matemáticos mais precisos de EEG.
Para atender a essa necessidade para gravações simultâneas explorar a origem neural do EEG, desenvolvemos uma metodologia para gravar simultaneamente EEG e multi-laminar LFP sinais no neocórtex do rato anestesiado. A instalação é semelhante de estudos anteriores de EEG/LFP simultâneos, realizados em primatas16,17. Investigamos mais o efeito de um orifício de trépano, perfurado o crânio em gravações de EEG em torno do furo, através da comparação bilaterais gravações de EEG (ou seja, um hemisfério com um orifício de trépano, o outro hemisfério intacto) na ausência de sensorial estimulação. Nossos resultados demonstram que gravações simultâneas de EEG/LFP podem efectuar-se simples e eficaz, com pouca distorção do sinal EEG da trepanação do crânio.

<table>
	<tbody>
		<tr>
			<td>Female Lister Hood rats</td>
			<td>Charles Rivers</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Spider electrode</td>
			<td>Unimed Electrode Supplies Ltd</td>
			<td>SCS24-426</td>
			<td></td>
		</tr>
		<tr>
			<td>EEG paste: Ten20</td>
			<td>Unimed Electrode Supplies Ltd</td>
			<td>10-20-S</td>
			<td></td>
		</tr>
		<tr>
			<td>Stereotaxic holder with dual micromanipulator arms: Dual Manipulator Stereotaxic Frame with 18&#176; Ear Bars</td>
			<td>WPI (World Precision Instruments)</td>
			<td>502603</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>National Vet Services Limited</td>
			<td>50878</td>
			<td></td>
		</tr>
		<tr>
			<td>Hard plastic nose cone: Anasthesia Gas Mask for Rat</td>
			<td>WPI</td>
			<td>502054</td>
			<td></td>
		</tr>
		<tr>
			<td>Small animal isoflurane anaesthetic system</td>
			<td>WPI</td>
			<td>EZ-B800A</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermostatic heating pad: Rat Blanket System 230V</td>
			<td>Harvard Apparatus UK</td>
			<td>50-7221-F</td>
			<td></td>
		</tr>
		<tr>
			<td>Ophthalmic ointment: Optixcare eye lube</td>
			<td>Viovet</td>
			<td>203865</td>
			<td></td>
		</tr>
		<tr>
			<td>Lidocaine Hydrochloride (Injection 2%)</td>
			<td>Larkmead Vets</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Jacquette Scaler #1SSE, 18cm, Hollow</td>
			<td>WPI</td>
			<td>503421</td>
			<td></td>
		</tr>
		<tr>
			<td>Serrated and curved dissecting forceps</td>
			<td>WPI</td>
			<td>15915</td>
			<td></td>
		</tr>
		<tr>
			<td>Braided silk, non-absorbable suture: Mersilk Suture W502H</td>
			<td>National Vet Services Limited</td>
			<td>153746</td>
			<td></td>
		</tr>
		<tr>
			<td>Dental drill: BONE MICRO DRILL SYST 230 VAC</td>
			<td>Harvard Apparatus UK</td>
			<td>72-4860</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile Saline: Sodium chloride 0.9%</td>
			<td>Animalcare Ltd</td>
			<td>14K26BT</td>
			<td></td>
		</tr>
		<tr>
			<td>Drill bit #4 : Ball Mill, Carbide, #4</td>
			<td>Harvard Apparatus UK</td>
			<td>72-4958</td>
			<td></td>
		</tr>
		<tr>
			<td>Drill bit #4 : Ball Mill, Carbide, #1/4</td>
			<td>Harvard Apparatus UK</td>
			<td>72-4962</td>
			<td></td>
		</tr>
		<tr>
			<td>Faraday cage</td>
			<td>Newport Corporation</td>
			<td>VIS-FDC-3600</td>
			<td></td>
		</tr>
		<tr>
			<td>Vibration isolation workstation: Vision IsoStation</td>
			<td>Newport Corporation</td>
			<td>M-VIS3660-RG4-325A</td>
			<td></td>
		</tr>
		<tr>
			<td>Oximeter Control Unit and sensor: MouseOxPlus, Starr Life Sciences Corp.</td>
			<td>WPI</td>
			<td>O15001</td>
			<td></td>
		</tr>
		<tr>
			<td>Transparent soft nose cone: Microflex Non-Rebreathing Unit with a Rat Nosecone</td>
			<td>WPI</td>
			<td>EZ-103A</td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless steel stimulating electrodes</td>
			<td>PlasticsOne</td>
			<td>E363/1/SPC</td>
			<td></td>
		</tr>
		<tr>
			<td>Isolated current stimulator</td>
			<td>Made in House</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>16-channel micro-electrode, 100 &#956;m spacing, area of each site 177 &#956;m2</td>
			<td>NeuroNexus</td>
			<td>A1x16-10mm-100-177-A16</td>
			<td></td>
		</tr>
		<tr>
			<td>16-channel acute headstage</td>
			<td>Tucker David Technologies Inc., TDT</td>
			<td>RA16AC-Z</td>
			<td></td>
		</tr>
		<tr>
			<td>Pre-Amplifier: Z-Series 64-Channel Neuro-Digitizing Preamp</td>
			<td>TDT</td>
			<td>PZ5-64</td>
			<td></td>
		</tr>
		<tr>
			<td>Passive signal splitter: 32-Channel Splitter Box for PZ5</td>
			<td>TDT</td>
			<td>S-BOX_PZ5</td>
			<td></td>
		</tr>
		<tr>
			<td>Data acquisition unit: RZ2 BioAmp Processor. Z-Series 4-DSP ultra high performance processor</td>
			<td>TDT</td>
			<td>RZ2-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Software for Neurophysiology: OpenEX</td>
			<td>TDT</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Matlab</td>
			<td>MathWorks</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Absorption spears</td>
			<td>Fine Sicence Tools</td>
			<td>18105-01</td>
			<td></td>
		</tr>
	</tbody>
</table>

concurrent recording of co-localized electroencephalography and local field potential in rodent

Apesar de eletroencefalografia (EEG) é amplamente utilizada como uma técnica não-invasiva para gravação de atividades neurais do cérebro, nosso entendimento sobre a neurogênese de EEG é ainda muito limitado. Potenciais de campo local (LFPs) gravados através de um microeléctrodo multi-laminar podem fornecer um relato mais detalhado da atividade neural simultânea em diferentes camadas corticais no neocórtex, mas a técnica é invasiva. Combinar medidas de EEG e LFP em um modelo pré-clínico pode extremamente aumentar a compreensão dos mecanismos neurais envolvidos na geração de sinais EEG e facilitar a derivação de um modelo matemático mais realista e biologicamente exato de EEG. Um procedimento simples para a aquisição de EEG simultâneo e co localizada e multi-laminar LFP sinais no roedor anestesiado é aqui apresentado. Também investigamos se sinais EEG foram significativamente afetados por um orifício de trépano, perfurado o crânio para a inserção de um microeléctrodo. Nossos resultados sugerem que a trepanação tem um impacto insignificante na gravações de EEG.

Dados de 4 ratos foram em média para obter o tempo médio série, quando aplicável. A amplitude da resposta evocada EEG, também conhecido como o evento relacionado potencial (ERP), é geralmente muito menor do que a LFP. A Figura 6 mostra a média ERP e LFP no supragranular, granular e infragranular camadas do córtex barril, respectivamente. A banda de erro em cada parcela é o erro-padrão correspondente. Pode ser visto que ERP é aproximadamente 10 vezes menor do que a LFP evocado.
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56447/56447fig6.jpg"> Figura 6: dizer (n = 4) sinais neurais de ERP, supragranular, granular e infragranular LFP. Sombra indica erro padrão. <a href="//cloudflare.jove.com/files/ftp_upload/56447/56447fig6large.jpg" target="_blank">Clique aqui para ver uma versão maior desta figura.</a>
Comparações da dinâmica temporal do ERP e LFP são mostradas na Figura 7. Superposição direta de ERP e o supragranular LFP na Figura 7A ilustra a ordem de amplitude as diferenças entre estes dois tipos de sinais neurais. Para comparar a dinâmica temporal, tanto o ERP e o LFP são normalizados em relação a sua amplitude de pico negativo. Figura 7B e 7C mostram que o ERP normalizado sobreposta com o supragranular normalizado LFP e normalizado LFP granular, respectivamente.
Pode ser visto a partir da Figura 7B que os picos de P1 e N1 para ERP são mais atrasados do que os picos correspondentes da LFP na camada supragranular. No entanto, os perfis temporais destes dois sinais neurais são semelhantes, com P1 anterior N1. Por outro lado, o perfil temporal de ERP é marcadamente diferente de granular (camada IV do córtex barril) LFP (Figura 7). Importante não são imagens espelhadas um do outro, com LFP granular, dominada por um único pico negativo (refletindo um dissipador grande na camada cortical IV), Considerando que o ERP consistia primariamente de dois picos com polaridade oposta.
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/56447/56447fig7.jpg"> Figura 7: comparação da dinâmica temporal do ERP e LFP. (A) ERP (linha sólida) sobreposto com supragranular LFP (linha tracejada). Sombra indica erro padrão. (B) normalizado ERP (linha sólida) sobreposto com supragranular normalizado LFP (linha tracejada). (C) normalizado ERP (linha sólida) sobreposto com LFP granular normalizado (linha tracejada). <a href="//cloudflare.jove.com/files/ftp_upload/56447/56447fig7large.jpg" target="_blank">Clique aqui para ver uma versão maior desta figura.</a>
O sinal ERP foi medido através de um eletrodo de aranha colocado no crânio com um orifício de trépano, perfurado-lo. Para investigar o efeito do buraco em gravações de EEG, outro eletrodo de aranha foi colocado no crânio intacto acima o córtex ipsi-lateral barril. Cuidado foi tomado para garantir que as impedâncias dos eléctrodos dois aranha eram comparáveis em magnitude ajustando a quantidade de EEG colar usado. Dados de quatro ratos (que foram não os ratos mesmos usados acima) são apresentados aqui.
A Figura 8 mostra as gravações simultâneas de descanso do EEG estado de ambos os eletrodos de um rato, com 100 dados exibidos na Figura 8Ae os dados no quadro retangular (20 s) são expandidas na Figura 8B. Os dois sinais de EEG em grande parte co variam, dentro da gama de amplitude semelhante. A Figura 9 mostra o PSD dos quatro ratos, com a linha superior usando uma escala linear no eixo de frequência e a linha de fundo, usando uma escala logarítmica no eixo de frequência para fornecer uma visão expandida na faixa de frequência mais baixa. Da Figura 9, não parece ser consistente viés no PSD através de temas. Isto foi confirmado por meio de uma amostra t-testes as diferenças normalizadas no PSD em média na faixa dos cinco, mostrado na Figura 10. Nenhuma das diferenças PSD normalizadas nessas bandas de frequência era significativamente diferente de zero (p = 0,32, 0.46, 0.85, 0,69 e 0,97, respectivamente).
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/56447/56447fig8.jpg"> Figura 8: gravações de EEG Bilateral. (A) crânio EEG gravação durante repouso estado com um orifício de trépano no crânio (preto) e um registro de EEG simultâneo no hemisfério oposto, com o crânio intacto (cinza). Expanded (B) vista de dentro do quadro retangular no (A) as formas de onda. <a href="//cloudflare.jove.com/files/ftp_upload/56447/56447fig8large.jpg" target="_blank">Clique aqui para ver uma versão maior desta figura.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/56447/56447fig9.jpg"> Figura 9: densidade espectral (PSD) de energia do contra-(azul) e o EEG ipsi-lateral (vermelho). Cada coluna mostra o PSD para um rato. Os painéis superiores usam a escala de frequência linear, enquanto os painéis de fundo usam escala logarítmica frequência para permitir que o PSD na faixa de frequência mais baixa para ser visualizado. <a href="//cloudflare.jove.com/files/ftp_upload/56447/56447fig9large.jpg" target="_blank">Clique aqui para ver uma versão maior desta figura.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/56447/56447fig10.jpg"> Figura 10: análise de grupo. Normalizada a diferença entre o contra - e o PSD ipsi-lateral com as bandas de cinco frequência: Delta, Theta, alfa, Beta e gama. Cada barra mostra as diferenças normalizadas médios dentro da faixa de frequência, com o erro-padrão mostrado como a barra de erro. <a href="//cloudflare.jove.com/files/ftp_upload/56447/56447fig10large.jpg" target="_blank">Clique aqui para ver uma versão maior desta figura.</a>

Watch this Scientific Journal Video about Concurrent Recording of Co-localized Electroencephalography and Local Field Potential in Rodent at JoVE.com

Concurrent Recording of Co-localized Electroencephalography and Local Field Potential in Rodent

Este protocolo descreve um método simples para gravação simultânea de co localizada Eletroencefalografia (EEG) e multi-laminar local campo potencial em um rato anestesiado. Um orifício de trépano, perfurado o crânio para a inserção de um microeléctrodo é mostrado para produzir distorção negligenciável do sinal EEG.

Gravação simultânea de eletroencefalografia co localizada e potencial do campo Local em roedores

Although electroencephalography (EEG) is widely used as a non-invasive technique for recording neural activities of the brain, our understanding of the ...

concurrent-recording-co-localized-electroencephalography-local-field

Research

JoVE Journal

Neuroscience

12.2K visualizações.  University of Reading. Este protocolo descreve um método simples para gravação simultânea de co localizada Eletroencefalografia (EEG) e multi-laminar local campo potencial em um rato anestesiado. Um orifício de trépano, perfurado o crânio para a inserção de um microeléctrodo é mostrado para produzir distorção negligenciável do sinal EEG.

Vídeo: Concurrent Recording of Co-localized Electroencephalography and Local Field Potential in Rodent

Systemic and Local Drug Delivery for Treating Diseases of the Central Nervous System in Rodent Models

Thorough preclinical testing of central nervous system (CNS) therapeutics includes a consideration of routes of administration and agent biodistribution in assessing therapeutic efficacy. Between the two major classifications of administration, local vs. systemic, systemic delivery approaches are often preferred due to ease of administration. However, systemic delivery may result in suboptimal drug concentration being achieved in the CNS, and lead to erroneous conclusions regarding agent efficacy. Local drug delivery methods are more invasive, but may be necessary to achieve therapeutic CNS drug levels. Here, we demonstrate proper technique for three routes of systemic drug delivery: intravenous injection, intraperitoneal injection, and oral gavage. In addition, we show a method for local delivery to the brain: convection-enhanced delivery (CED). The use of fluorescently-labeled compounds is included for in vivo imaging and verification of proper drug administration. The methods are presented using murine models, but can easily be adapted for use in rats.

Thorough preclinical testing of drugs that act in the central nervous system often involves assessing and comparing drug biodistribution in association with specific routes of administration. Here, three commonly used methods of systemic delivery (intravenous, intraperitoneal, and oral) as well as a method for local delivery (convection-enhanced delivery) are demonstrated in mice.

Entrega da droga sistêmica e local para o tratamento de doenças do sistema nervoso central em modelos de roedores

Thorough preclinical testing of central nervous system (CNS) therapeutics includes a consideration of routes of administration and agent biodistribution ...

Neurociência

Examining Local Network Processing using Multi-contact Laminar Electrode Recording

Cortical layers are ubiquitous structures throughout neocortex1-4 that consist of highly recurrent local networks. In recent years, significant progress has been made in our understanding of differences in response properties of neurons in different cortical layers5-8, yet there is still a great deal left to learn about whether and how neuronal populations encode information in a laminar-specific manner.
Existing multi-electrode array techniques, although informative for measuring responses across many millimeters of cortical space along the cortical surface, are unsuitable to approach the issue of laminar cortical circuits. Here, we present our method for setting up and recording individual neurons and local field potentials (LFPs) across cortical layers of primary visual cortex (V1) utilizing multi-contact laminar electrodes (Figure 1; Plextrode U-Probe, Plexon Inc).
The methods included are recording device construction, identification of cortical layers, and identification of receptive fields of individual neurons. To identify cortical layers, we measure the evoked response potentials (ERPs) of the LFP time-series using full-field flashed stimuli. We then perform current-source density (CSD) analysis to identify the polarity inversion accompanied by the sink-source configuration at the base of layer 4 (the sink is inside layer 4, subsequently referred to as granular layer9-12). Current-source density is useful because it provides an index of the location, direction, and density of transmembrane current flow, allowing us to accurately position electrodes to record from all layers in a single penetration6, 11, 12.

A fundamental issue in our understanding of cortical circuitry is how networks in different cortical layers encode sensory information. Here we describe electrophysiological techniques utilizing multi-contact laminar electrodes to record single-units and local field potentials and present analyses to identify cortical layers.

Examinando Processamento Rede Local usando contato Multi-Gravação Eletrodo Laminar

Cortical layers are ubiquitous structures throughout neocortex1-4 that consist of highly recurrent local networks. In recent years, significant progress ...

Simultaneous Electroencephalography, Real-time Measurement of Lactate Concentration and Optogenetic Manipulation of Neuronal Activity in the Rodent Cerebral Cortex

Although the brain represents less than 5% of the body by mass, it utilizes approximately one quarter of the glucose used by the body at rest1. The function of non rapid eye movement sleep (NREMS), the largest portion of sleep by time, is uncertain. However, one salient feature of NREMS is a significant reduction in the rate of cerebral glucose utilization relative to wakefulness2-4. This and other findings have led to the widely held belief that sleep serves a function related to cerebral metabolism. Yet, the mechanisms underlying the reduction in cerebral glucose metabolism during NREMS remain to be elucidated.
	One phenomenon associated with NREMS that might impact cerebral metabolic rate is the occurrence of slow waves, oscillations at frequencies less than 4 Hz, in the electroencephalogram5,6. These slow waves detected at the level of the skull or cerebral cortical surface reflect the oscillations of underlying neurons between a depolarized/up state and a hyperpolarized/down state7. During the down state, cells do not undergo action potentials for intervals of up to several hundred milliseconds. Restoration of ionic concentration gradients subsequent to action potentials represents a significant metabolic load on the cell8; absence of action potentials during down states associated with NREMS may contribute to reduced metabolism relative to wake.
	Two technical challenges had to be addressed in order for this hypothetical relationship to be tested. First, it was necessary to measure cerebral glycolytic metabolism with a temporal resolution reflective of the dynamics of the cerebral EEG (that is, over seconds rather than minutes). To do so, we measured the concentration of lactate, the product of aerobic glycolysis, and therefore a readout of the rate of glucose metabolism in the brains of mice. Lactate was measured using a lactate oxidase based real time sensor embedded in the frontal cortex. The sensing mechanism consists of a platinum-iridium electrode surrounded by a layer of lactate oxidase molecules. Metabolism of lactate by lactate oxidase produces hydrogen peroxide, which produces a current in the platinum-iridium electrode. So a ramping up of cerebral glycolysis provides an increase in the concentration of substrate for lactate oxidase, which then is reflected in increased current at the sensing electrode. It was additionally necessary to measure these variables while manipulating the excitability of the cerebral cortex, in order to isolate this variable from other facets of NREMS.
	We devised an experimental system for simultaneous measurement of neuronal activity via the elecetroencephalogram, measurement of glycolytic flux via a lactate biosensor, and manipulation of cerebral cortical neuronal activity via optogenetic activation of pyramidal neurons. We have utilized this system to document the relationship between sleep-related electroencephalographic waveforms and the moment-to-moment dynamics of lactate concentration in the cerebral cortex. The protocol may be useful for any individual interested in studying, in freely behaving rodents, the relationship between neuronal activity measured at the electroencephalographic level and cellular energetics within the brain.

A procedure is described for manipulating the activity of cerebral cortical pyramidal neurons optogenetically while the electroencephalogram, electromyogram, and cerebral lactate concentration are monitored. Experimental recordings are performed on cable-tethered mice while they undergo spontaneous sleep/wake cycles. Optogenetic equipment is assembled in our laboratory; recording equipment is commercially available.

Eletroencefalografia simultânea, em tempo real de medição da concentração de lactato e Manipulação optogenética da atividade neuronal do córtex cerebral de roedores

Although the brain represents less than 5% of the body  by mass, it utilizes approximately one quarter of the glucose used by the body  at rest1. The ...

Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis

The freshwater leech, Hirudo medicinalis, is a versatile model organism that has been used to address scientific questions in the fields of neurophysiology, neuroethology, and developmental biology. The goal of this report is to consolidate experimental techniques from the leech system into a single article that will be of use to physiologists with expertise in other nervous system preparations, or to biology students with little or no electrophysiology experience. We demonstrate how to dissect the leech for recording intracellularly from identified neural circuits in the ganglion. Next we show how individual cells of known function can be removed from the ganglion to be cultured in a Petri dish, and how to record from those neurons in culture. Then we demonstrate how to prepare a patch of innervated skin to be used for mapping sensory or motor fields. These leech preparations are still widely used to address basic electrical properties of neural networks, behavior, synaptogenesis, and development. They are also an appropriate training module for neuroscience or physiology teaching laboratories.

Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis

This article describes three nervous system preparations using leeches: intracellular recording from neurons in ventral ganglia, culturing neurons from ventral ganglia, and recording from a patch of innervated skin to map sensory fields.

Intracelular de gravação, Sensorial Campo Mapping, e cultivando neurônios identificados nos Sanguessuga, Hirudo medicinalis</i

The freshwater leech, Hirudo medicinalis, is a versatile model organism that has been used to address scientific questions in the fields of ...

Measuring Spinal Presynaptic Inhibition in Mice By Dorsal Root Potential Recording In Vivo

Presynaptic inhibition is one of the most powerful inhibitory mechanisms in the spinal cord. The underlying physiological mechanism is a depolarization of primary afferent fibers mediated by GABAergic axo-axonal synapses (primary afferent depolarization). The strength of primary afferent depolarization can be measured by recording of volume-conducted potentials at the dorsal root (dorsal root potentials, DRP). Pathological changes of presynaptic inhibition are crucial in the abnormal central processing of certain pain conditions and in some disorders of motor hyperexcitability. Here, we describe a method of recording DRP in vivo in mice. The preparation of spinal cord dorsal roots in the anesthetized animal and the recording procedure using suction electrodes are explained. This method allows measuring GABAergic DRP and thereby estimating spinal presynaptic inhibition in the living mouse. In combination with transgenic mouse models, DRP recording may serve as a powerful tool to investigate disease-associated spinal pathophysiology. In vivo recording has several advantages compared to ex vivo isolated spinal cord preparations, e.g. the possibility of simultaneous recording or manipulation of supraspinal networks and induction of DRP by stimulation of peripheral nerves.

Measuring Spinal Presynaptic Inhibition in Mice By Dorsal Root Potential Recording In Vivo

GABAergic presynaptic inhibition is a powerful inhibitory mechanism in the spinal cord important for motor and sensory signal integration in spinal cord networks. Underlying primary afferent depolarization can be measured by recording of dorsal root potentials (DRP). Here we demonstrate a method of in vivo recording of DRP in mice.

Medindo Spinal pré-sináptica Inibição em Ratos por raiz dorsal Gravação Potencial<em&gt; In Vivo</em

Presynaptic inhibition is one of the most powerful inhibitory mechanisms in the spinal cord. The underlying physiological mechanism is a depolarization of ...

Simultaneous Electrophysiological Recording and Micro-injections of Inhibitory Agents in the Rodent Brain

Here we describe a method for the construction of a single-use &#8220;injectrode&#8221; using commercially accessible and affordable parts. A probing system was developed that allows for the injection of a drug while recording electrophysiological signals from the affected neuronal population. This method provides a simple and economical alternative to commercial solutions. A glass pipette was modified by combining it with a hypodermic needle and a silver filament. The injectrode is attached to commercial microsyringe pump for drug delivery. This results in a technique that provides real-time pharmacodynamics feedback through multi-unit extracellular signals originating from the site of drug delivery. As a proof of concept, we recorded neuronal activity from the superior colliculus elicited by flashes of light in rats, concomitantly with delivery of drugs through the injectrode. The injectrode recording capacity permits the functional characterization of the injection site favoring precise control over the localization of drug delivery. Application of this method also extends far beyond what is demonstrated here, as the choice of chemical substance loaded into the injectrode is vast, including tracing markers for anatomic experiments.

Here, we craft a glass pipette with dual functions: inhibition of deep brain structures by microinjections of drugs and real-time monitoring of their effects through simultaneous electrophysiological recordings.

Gravação simultânea eletrofisiológica e micro-injeções de agentes inibidores no cérebro do roedor

Here we describe a method for the construction of a single-use &#8220;injectrode&#8221; using commercially accessible and affordable parts. A probing ...

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the pathophysiological basis of these diseases, it is necessary to precisely characterize in which way the processing of information is disturbed between the different neuronal parts of the circuit. Using extracellular in vivo electrophysiological recordings, it is possible to accurately delineate neuronal activity within a neuronal network. The application of this method has several advantages over alternative techniques, e.g., functional magnetic resonance imaging and calcium imaging, as it allows a unique temporal and spatial resolution and does not rely on genetically engineered organisms. However, the use of extracellular in vivo recordings is limited since it is an invasive technique that cannot be universally applied. In this article, a simple and easy to use method is presented with which it is possible to simultaneously record extracellular potentials such as local field potentials and multiunit activity at multiple sites of a network. It is detailed how a precise targeting of subcortical nuclei can be achieved using a combination of stereotactic surgery and online analysis of multi-unit recordings. Thus, it is demonstrated, how a complete network such as the hyperdirect cortico-basal ganglia loop can be studied in anesthetized animals in vivo.

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

In this study, the methodology is presented on how to perform multi-site in vivo electrophysiological recordings from the hyperdirect pathway under urethane anesthesia.

Agudo<em&gt; In Vivo</em&gt; Gravações eletrofisiológicas de Potenciais de campo locais e atividade de múltiplas unidades a partir do caminho hiperdiretivo em ratos anestesiados

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the ...

Recording and Modulation of Epileptiform Activity in Rodent Brain Slices Coupled to Microelectrode Arrays

Temporal lobe epilepsy (TLE) is the most common partial complex epileptic syndrome and the least responsive to medications. Deep brain stimulation (DBS) is a promising approach when pharmacological treatment fails or neurosurgery is not recommended. Acute brain slices coupled to microelectrode arrays (MEAs) represent a valuable tool to study neuronal network interactions and their modulation by electrical stimulation. As compared to conventional extracellular recording techniques, they provide the added advantages of a greater number of observation points and a known inter-electrode distance, which allow studying the propagation path and speed of electrophysiological signals. However, tissue oxygenation may be greatly impaired during MEA recording, requiring a high perfusion rate, which comes at the cost of decreased signal-to-noise ratio and higher oscillations in the experimental temperature. Electrical stimulation further stresses the brain tissue, making it difficult to pursue prolonged recording/stimulation epochs. Moreover, electrical modulation of brain slice activity needs to target specific structures/pathways within the brain slice, requiring that electrode mapping be easily and quickly performed live during the experiment. Here, we illustrate how to perform the recording and electrical modulation of 4-aminopyridine (4AP)-induced epileptiform activity in rodent brain slices using planar MEAs. We show that the brain tissue obtained from mice outperforms rat brain tissue and is thus better suited for MEA experiments. This protocol guarantees the generation and maintenance of a stable epileptiform pattern that faithfully reproduces the electrophysiological features observed with conventional field potential recording, persists for several hours, and outlasts sustained electrical stimulation for prolonged epochs. Tissue viability throughout the experiment is achieved thanks to the use of a small-volume custom recording chamber allowing for laminar flow and quick solution exchange even at low (1 mL/min) perfusion rates. Quick MEA mapping for real-time monitoring and selection of stimulating electrodes is performed by a custom graphic user interface (GUI).

We illustrate how to perform recording and electrical modulation of 4-aminopyridine-induced epileptiform activity in rodent brain slices using microelectrode arrays. A custom recording chamber maintains tissue viability throughout prolonged experimental sessions. Live electrode mapping and selection of stimulating pairs are performed by a custom graphical user interface.

Gravação e modulação da atividade epileptiforme em fatias de cérebro de roedor acoplado para matrizes de microeletrodos

Temporal lobe epilepsy (TLE) is the most common partial complex epileptic syndrome and the least responsive to medications. Deep brain stimulation (DBS) ...

Evaluation of Hemisphere Lateralization with Bilateral Local Field Potential Recording in Secondary Motor Cortex of Mice

This article demonstrates complete, detailed procedures for both in vivo bilateral recording and analysis of local field potential (LFP) in the cortical areas of mice, which are useful for evaluating possible laterality deficits, as well as for assessing brain connectivity and coupling of neural network activities in rodents. The pathological mechanisms underlying Alzheimer&#39;s disease (AD), a common neurodegenerative disease, remain largely unknown. Altered brain laterality has been demonstrated in aging people, but whether or not abnormal lateralization is one of the early signs of AD has not been determined. To investigate this, we recorded bilateral LFPs in 3-5-month-old AD model mice, APP/PS1, together with littermate wild type (WT) controls. The LFPs of the left and right secondary motor cortex (M2), specifically in the gamma band, were more synchronized in APP/PS1 mice than in WT controls, suggesting a declined hemispheric asymmetry of bilateral M2 in this AD mouse model. Notably, the recording and data analysis processes are flexible and easy to carry out, and can also be applied to other brain pathways when conducting experiments that focus on neuronal circuits.

We present in vivo electrophysiological recording of the local field potential (LFP) in bilateral secondary motor cortex (M2) of mice, which can be applied to evaluate hemisphere lateralization. The study revealed altered levels of synchronization between the left and right M2 in APP/PS1 mice compared to WT controls.

Avaliação da lateralização do hemisfério com registro de potencial de campo local bilateral no córtex motor secundário de camundongos

This article demonstrates complete, detailed procedures for both in vivo bilateral recording and analysis of local field potential (LFP) in the cortical ...

Investigating Long-term Synaptic Plasticity in Interlamellar Hippocampus CA1 by Electrophysiological Field Recording

The study of synaptic plasticity in the hippocampus has focused on the use of the CA3-CA1 lamellar network. Less attention has been given to the longitudinal interlamellar CA1-CA1 network. Recently however, an associational connection between CA1-CA1 pyramidal neurons has been shown. Therefore, there is the need to investigate whether the longitudinal interlamellar CA1-CA1 network of the hippocampus supports synaptic plasticity.
We designed a protocol to investigate the presence or absence of long-term synaptic plasticity in the interlamellar hippocampal CA1 network using electrophysiological field recordings both in vivo and in vitro. For in vivo extracellular field recordings, the recording and stimulation electrodes were placed in a septal-temporal axis of the dorsal hippocampus at a longitudinal angle, to evoke field excitatory postsynaptic potentials. For in vitro extracellular field recordings, hippocampal longitudinal slices were cut parallel to the septal-temporal plane. Recording and stimulation electrodes were placed in the stratum oriens (S.O) and the stratum radiatum (S.R) of the hippocampus along the longitudinal axis. This enabled us to investigate the directional and layer specificity of evoked excitatory postsynaptic potentials. Already established protocols were used to induce long-term potentiation (LTP) and long-term depression (LTD) both in vivo and in vitro. Our results demonstrated that the longitudinal interlamellar CA1 network supports N-methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation (LTP) with no directional or layer specificity. The interlamellar network, however, in contrast to the transverse lamellar network, did not present with any significant long-term depression (LTD).

We used recording and stimulation electrodes in longitudinal hippocampal brain slices and longitudinally positioned recording and stimulation electrodes in the dorsal hippocampus in vivo to evoke extracellular postsynaptic potentials and demonstrate long-term synaptic plasticity along the longitudinal interlamellar CA1.