We also divide the trials into two categories: a correct trial is one in which the two cards revealed a matching pair and an incorrect trial indicates that the subject chose nonmatching cards. After the recording session, the local field potential data were extracted for each mouse click on a card, which coincided HA-1077 price with the presentation of the image stimulus. The segments of data were approximately four seconds long, centered on
each click (±2 s). This length was chosen to avoid edge effects in the time range of interest, which was ±1 s around the stimulus presentation. After resampling at 2 kHz, we removed the mean of each data segment during the presentation of the stimulus. No other filtering was done on the data. We utilized the free WaveLab toolbox for MATLAB (Donoho et al., 2005) to perform the wavelet analysis. More specifically, we used the “CWT_Wavelab” function to do a continuous wavelet transform. We chose a complex Morlet wavelet with the following time domain representation: ψ(t)=e−12t2(eiω0t−e−12ω02).Or equivalently in the Fourier Cobimetinib price domain, ψˆ(ω)=e−12(ω−ω0)2−e−12(ω2+ω02),with ω0=5ω0=5 representing the number of cycles in the wavelet. For the WaveLab function, we chose parameters nvoice = 10, scale = 4, and oct = 6. These settings allowed us to analyze 70 frequencies,
ranging from 0.87 Hz to 103.97 Hz (the frequencies varied by 0.1 from −0.2 to 6.7 on a logarithmic scale of base 2). The exact length of each data segment was 8,192 data points (4.096 s at 2 kHz) to fulfill the requirement of an input signal with dyadic length. The result of convolving the Morlet wavelet with our LFP data was a complex signal Z(t). We used this to calculate both the instantaneous amplitude A(t)=Re[Z(t)]2+Im[Z(t)]2and the instantaneous phase φ(t)=arctan(Im[Z(t)]Re[Z(t)]). These equations are equivalent to the “abs” and “angle” functions
in MATLAB. The phase spanned the range [−π, π] with zero being the peak of the oscillation. As a measure of the baseline activity in each data set, we calculated the average instantaneous amplitude A¯ over 1,000 randomly selected segments of data. Then, using the standard deviation of amplitude σAσA over the 1,000 segments and Rutecarpine the number of trials n, we were able to represent the amplitude as a Z score based on the statistics of the population: A˜(t)=A(t)−A¯σAn. The goal of single trial classification is to determine how accurately we can divide single trials of LFP data into two categories based on whether they were triggered on a correct response (matching cards) or an incorrect response (nonmatching cards). We begin by using the first data set (ten puzzles with a total of 80 correct trials) to calculate the classifier. Given this limited data set, we chose a linear classifier. For all LFP responses in the data set, we determine the mean of the correct trials a¯ and the mean of the incorrect trials b¯, and we define the classifier to be b¯−a¯.