1. Two Mean Neuronal Waveforms Distribution of Spike Widths Interaction of Inhibitory and Excitatory Neurons During Visual Stimulation David Maher Department of Neurobiology and Anatomy, University of Texas Houston Medical School, TX 77030 An unsolved problem in neuroscience is how inhibitory and excitatory neurons interact in the context of their local network. Without inhibitory neurons there would be an epileptic runaway excitation, so inhibitory neurons preserve stability in cortical networks. We recorded neuronal activity in the primary visual cortex (V1) of a macaque monkey using multiple electrodes. The inhibitory and excitatory neurons were separated so that noise correlations could be measured. Measuring noise correlations between different populations of cells will improve our knowledge of how inhibitory and excitatory neurons interact. Introduction Methods 11 trials of extracellular multiple-electrode recordings in awake macaque primary visual cortex (V1). Target stimulus – 300 ms picture of sine-wave grating at either 45° or 135°. Test stimulus – 300 ms picture of sine-wave grating 0°,5°, or 10° different from target stimulus. Task – Macaque lifts bar when target and test stimulus are the same angle. Inhibitory and Excitatory Neurons separated by a spike width of 200 ms. 138 neurons were examined. 71 Inhibitory Neurons 67 Excitatory Neurons Sine-Wave Grating Mean Neuronal Waveforms 30 Individual Waveforms Figure 1. (A) Average waveform of all Inhibitory and Excitatory neurons. (B) 30 individual mean Excitatory and Inhibitory waveforms. Figure 3. Distribution of spike widths. A B Analysis Immediate increase in number of spikes/s when target and test stimuli are produced. Inhibitory cells have higher spontaneous firing rates. Excitatory cells have higher firing rates during stimuli events. Excitatory PSTH Inhibitory PSTH Figure 4. PSTH – Post-stimulus time histogram: Firing rates (number of spikes/s) for every millisecond of the trial. Average PSTH for (A) Excitatory and (B) Inhibitory neurons in the same trial. A B Test Stimulus Test Stimulus Target Stimulus Target Stimulus Further Research Compute noise correlation between excitatory and inhibitory cells for each trial. Asses impact of noise correlations on behavioral performance Figure 2. Two mean neuronal Waveforms from the same trial. Spike Width InhibitoryExcitatory Spike Width 350 ms 170 ms Spontaneous Firing Rate Spontaneous Firing Rate

2. Target Stimulus – 45° 300 ms Test Stimulus – 55 ° 300 ms Monkey holds on to bar Target Stimulus – 45° 300 ms Test Stimulus – 45 ° 300 ms Monkey releases bar Same Angle Different Angle

4. Spike Width 250 ms 100 ms +/- 1/2 Standard Deviation

5. Spike Width