The overall goal of this methodology is to monitor neural activations associated with the vocal production of consonant and dissonant intervals, through the use of functional magnetic resonance imaging. This method can help answer key questions in the field of auditory cognitive neuroscience, such as, how does integration of external feedback from the auditory and sensory motor systems differ when singing consonant and dissonant intervals? The main advantage of this technique is that it is designed to track activity of both the motor and the auditory system, while simultaneously obtaining a measure of vocal accuracy during singing.
Generally, individuals new to this method will struggle because it is difficult to record some tones faithfully from within the scanner as the entirety of the scanner is extremely noisy. Demonstrating the procedure will be Lucero Pacheco, a grad student from my laboratory. To begin producing pure tones spanning two octaves from G four to G six, open a new project folder in sound editing software.
Then, under the generate menu select tone. In the window that appears, select a sine waveform, an amplitude of 0.8, and a duration of one second. Enter the value of the frequency that corresponds to the desired note and click on the okay button.
Under the file menu select export. In the window that open enter the desired name for the audio file and choose wav as the desired file type. Click save.
Next, generate all possible combinations of notes corresponding to two consonant and two dissonant intervals in the range between G four and G six. To do this for each interval open a new project in the sound editing software and choose import audio under the file menu to import the two wav files to be concatenated. Place the cursor at any point over the second tone and click to select.
Click on select all under the edit menu. Under the same menu click on copy. Then, place the cursor at any point over the first tone and click.
Under the edit menu, click on move cursor to track end and then click paste under the same menu. Finally, under the file menu select export. In the window that opens enter the desired name for the audio file and choose wav as the desired file type.
Click save. Begin by having the participant sit down in front of a laptop computer and wear the provided headphones. Ensure that the sound level is comfortable for the participant.
Use behavioral research software to open two previously created tasks with e-run. In the window that appears enter the session and subject Number and click okay. Then, for the two alternative force choice tasks, ask the participants to identify whether the intervals they hear are consonant or dissonant by pressing either c on the computer keyboard for consonant and d for dissonant.
Next, in the four alternative force choice tasks have the participants identify the intervals themselves by pressing the numerals four, five, seven, and eight on the computer keyboard, to identify the intervals of an augmented fourth. Perfect fifth. Major seventh.
And octave respectively. Finally, at the end of each task press okay to automatically save the results for each participant. Begin by connecting a non-magnetic, MR compatible headset to a laptop, and ensure the sound level is comfortable for the participant.
Then, connect a small condenser microphone to an audio interface that is in turn connected to the laptop using a shielded, twisted, triplet cable. To check the microphone frequency response, start a new project in the sound editing software and select the condenser microphone as the input device. Then, generate a 440 hertz test tone with a duration of 10 seconds.
After the tone is generated, use sound reproduction software to press play to send the test tone through the headphones to two locations. Inside on top of the head rest and outside of the scanner in the control room with the microphone placed between the sides of the headset in each case. Next, press record in the sound editing software to record approximately one second of the test tone at each location.
Then, select plot spectrum from the analyze menu for each case and compare the response of the microphone to the test tone, both inside and outside the scanner by checking that the fundamental frequency of the signal received at each location is 440 hertz. Finally, tape the condenser microphone to the participant's neck just below the larynx, and have them wear the headset. Then, place the participant in the magnetic resonance scanner.
Begin by opening the magnetic resonance user interface MRUI software package. Within the MRUI software select the patient option from the onscreen menu. Enter the participant's name, age and weight.
Then, click on the exam button. First, choose head and then brain from the available options. Next, select 3D and then T1 isometric with the following values for the relevant parameters:repetition time equals 10.2 milliseconds, echo time equals 4.2 milliseconds, flip angle equals 90 degrees, and voxel size equals one by one by one millimeters cubed.
Then, click on program and begin the acquisition of the functional T2 star weighted whole head scan with the values of the relevant parameters as follows:TE equals 40 milliseconds, TR equals three seconds, field of view equals 256 millimeters squared, flip angle equals 90 degrees, matrix dimensions equal 64 by 64, delay in TR equals seven seconds. Note that in this case TR is the total time during which the acquisition takes place. Use the dummy option to acquire five volumes while entering a value of 55 for the total number of volumes.
Click copy to make a copy of this sequence. Place the cursor at the bottom of the list of sequences and then click paste twice to set up three consecutive sparse sampling sequences. Then, click start to begin the T1 weighted anatomical volume acquisition.
Finally, present three runs to the participant. Synchronize the start of the runs with the acquisition by the scanner using the scanner trigger box and differentiate between each run using the session number. Then, save the results of each run.
This study identified neural activity during singing in the regions known to constitute the singing network, which match those reported in prior literature. Results from a two way repeated measures analysis of variance indicated that for the contrast resulting from singing dissonant as opposed to consonant intervals, increased activations were observed in the right primary somatosensory cortex, right primary auditory cortex, left midbrain, right posterior insula, left amygdala, and left putamen. Once mastered, this technique can be done in four hours per subject.
If it is performed properly, taking into account, the behaviors test, the fMRI session, and the data analysis. While attempting this procedure, it is important to remember to check that the recording equipment is functioning correctly and to instruct the participants clearly that they should sing by humming, moving their heads as little as possible to avoid artifacts. Following this procedure, which is used to track differences in brain activation between binary conditions, a modified version of the method can be performed in order to study, for example, differences between singing wide and narrow intervals.
After each development the fMRI technique paves the way for researchers in the field of auditory neuroscience to explore neural mechanisms associated with audition and vocal production. After watching this video, you should have a good understanding of how to use fMRI to monitor the activity of both the motor and auditory systems during singing, in order to study the neural correlates of vocal production. Don't forget that working with a magnetic resonance scanner can be extremely hazardous and great care should always be taken to keep metallic objects away from the scanner.
