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| Paper IPM / Cognitive / 13877 |
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Sensory adaptation is an important physiological phenomenon that results from repeated stimulation of sensory
neurons in the brain but whose mechanisms remains poorly understood. Here, we measured the effect of visual
adaptation on the spontaneous activity of single neurons in the primary visual cortex of awake behaving primates. We used chronically-implanted ultra-thin electrodes with impedances of 1 to 3 MO (Swadlow et ai, 2005; Lashgari et ai, 2012) in area V1 of awake primates to measure local field potentials (LFPs) and the activity of neighboring single-unit (SU) simultaneously recorded with the same electrode tip. We measured neuronal responses before and after stimulation with a grating drifting at the preferred orientation for 2-3 sec at 2 Hz (usually 4 trials). We analyzed 109 single neurons and found 55 neurons that had a significant reduction in spontaneous activity following stimulation with the preferred stimulus orientation (mean reduction in firing rate: 7.5 SPK/sec; p<0.001, Sign rank test). To estimate the cortical depth of the recordings, we measured the polarity of the LFP integrated between 0 and 60 ms following the stimulus onset (Lashgari et ai, 2012; Li et ai, 2014). We found that reductions in spontaneous firing rate after adaptation could be demonstrated in cortical layers with both positive and negative LFP polarities. To investigate the types of neurons that were most affected by sensory adaptation, we measured the width of spike waveform from the spike onset (initial deflection from baseline) to the maximum amplitude. We found that reductions in the spontaneous firing rate with sensory adaptation could be demonstrated in neurons with different spike widths. We conclude that sensory adaptation can cause a reduction in the spontaneous firing rate of neurons in the awake primary visual cortex and that this reduction affects different types of neurons located in different cortical layers.
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