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Abstract:
Natural stimuli have a rich temporal structure, yet it is still unclear whether the encoding of such stimuli employs more than one response time scale. We investigated this issue by analyzing the activity of neurons recorded in primary visual cortex of anesthetized macaques during presentation of naturalistic color movies following procedures detailed in [1] and we quantified the amount of information carried by neural codes operating at different temporal scales. We divided the recording time into stimulus windows of 16-80 ms, and we computed the
information carried by the neural response about which stimulus window was being shown. First we measured the information carried by the total number of spikes in the stimulus window (spike count). Then we measured the information carried by the temporal pattern of spikes, computed by subdividing each stimulus window into time bins of size t and considering the binary spike train given by the absence/presence of spikes inside each bin. The information conveyed by temporal spike patterns with a t of 8 or 16 ms was up to 20% more than that conveyed by the spike count. This information gain did not increase further when considering resolutions finer than 8 ms, indicating that this is the precision of the spike patterns code. Coherently with the results of [2], we found that spike patterns carried information complementary to that carried by the phase of firing by quantifying if the joint knowledge of the spike pattern and the LFP phase of firing carried more information than either code considered alone. The information gained by the simultaneous knowledge of the phase of low frequency LFPs and of the spike patterns was 50% higher than the information carried by spike patterns alone and 15% higher than the information carried by the phase of firing alone. This suggests that the information carried by slow LFP fluctuations complements that carried by spike patterns.
In summary, we found evidence for complementary response time scales for the encoding of naturalistic stimuli in visual cortex. Informative codes range from spike timing precision at 10ms resolution to the much coarser phase of firing with respect to low frequency fluctuations. These
findings indicate that sensory cortices may enhance their information capacity by multiplexing complementary information at different time scales.
