This standard neurophysiological recording system can be used to perform a closed-loop stimulation which is useful for studying causal interactions in the brain. This protocol allows neuroscientists with only limited expertise in computer science to rapidly implement a variety of closed-loop experiments with little cost. Closed-loop experiments have becaming increasingly important for basic science and research.
For instance, multiple epilepsy studies have shown that neuron stimulation trigger on seizure onset is an an effective approach to reduce the severity of seizures. To facilitate the adoption of closed-loop experiments in neuroscience research, this protocol provides MATLAB code to convert an open-loop electrophysiological recording system into a closed-loop system. This implementation of closed-loop stimulation is demonstrated in an awake rat.
To install the Cheetah 6.4 Data Acquisition System, open the webpage for the software which includes libraries to interact with the Cheetah acquisitions system, and install SpikeSort-3D. Install the NetCom Development Package. Login to a MATLAB account to select the correct license, version, and operating system.
Then, download the library for online event triggering as indicated and extract the files to the documents MATLAB folder. For data acquisition, open the Cheetah software and record spiking data to populate the template waveforms. After a few minutes, stop the data acquisition and perform a SpikeSort on the recorded data.
Next, open SpikeSort3-D and click file menu and load spike file To select a spike file from the folder with the recorded data. Then, click cluster menu, autocluster using KlustaKwik, and run. To perform a closed-loop experiment, resume the data acquisition in Cheetah, and open MATLAB.
Open ClosedLoop. M and click run. Alternatively, execute closed-loop in the command window.
Browse to the recording folder and select one of the spiking data files to load the spike information defined in the initial recording. Click the appropriate check boxes under the plotted waveforms to select one or multiple neurons that will trigger stimulation. Define the minimum number of neurons that will trigger stimulation by entering an integer in the min matches text box and define the time window in which the spikes matching the different waveforms are considered coactive by entering a number into the window text box.
Then, click send to begin the online triggering of events based on the spiking activity of the selected neurons. In this representative experiment, the rat was rested on a flower pot which was a familiar resting place during breaks in the behavioral experiments. Here, a representative simultaneous running of the recording software and the MATLAB program which displays spike waveforms acquired in real time can be observed.
When spikes from predefined triggering clusters are detected, the waveforms are displayed with a bold dash line in the MATLAB figure window triggering a tone and providing a closed-loop system. In this figure, a representative histogram illustrating the delays between the time of generating an artificial spike and the time of inducing a triggered signal are shown. After preparing an animal, and installing the software, the closed-loop experiment consists of two main stages, the initial data acquisition and the closed-loop stimulation during which spikes trigger external stimuli.
This protocol also allows the treating of a stimuli based on the activity of multiple neurons which is important for addressing questions about information processing in the brain. The advantages of this MATLAB solution are its low cost and flexibility in defining the activity patterns to trigger stimuli which can help in investigating a variety of neuroscientific questions.
