Stimulus-suppressed neuronal responses in macaque visual cortex

FERNANDEZ LEON, J.A.; POJOGA, S.; DRAGOI, V.

California

Conferencia; 2013 SfN Neuroscience; 2013

SfN

The consensus in visual neurophysiology is that cells in visual cortex should increase their responses when stimulated in their receptive fields. However, several lines of evidence report deviations to the general dogma. It has been reported that some cat and rabbit retinal ganglion cells, as well as macaque lateral geniculate nucleus neurons, abruptly reduce or cease spiking activity when a visual stimulus is presented. Whether and how these ?stimulus-suppressed? cells have an effect on information coding in neural populations in visual cortex, and its relationship with behavior, is unknown. Here we performed multiple-electrode recordings in visual cortex (areas V1 and V4) of alert macaque using laminar electrodes (Plexon U-probes) to examine this particular type of cell and determine its properties. We found that stimulus-suppressed cells represent a small percentage (approximately 5%) of the total number of individual neurons and exhibit a wide range of suppression of baseline firing during stimulus presentation (suppression index range 0.2-0.9). This suppression has been observed using both oriented gratings and natural images and did not show stimulus selectivity or attentional modulation. We also found that suppression does not change with respect to the animal?s behavioral performance in an orientation discrimination task. Furthermore, based on waveform analysis, we assessed that the majority of these cells (>60%) are putative inhibitory neurons. Using CSD analysis, we determined that these rarely encountered neurons are evenly distributed across supragranular, infragranular and granular layers. We suggest that stimulus-suppressed cells contribute to the increase in the signal-to-noise ratio of visually responsive cells by reducing their firing before stimulus presentation. Overall, our results challenge current theories of sensory coding that will need to explain the functional significance of stimulus-suppressed neurons.