Despite progress in systems neuroscience the neural code still remains
elusive. For instance, the responses of single neurons are both highly
variable and ambiguous (similar responses can be elicited by different types
of stimuli). This variability/ambiguity has to be resolved by considering
the joint pattern of firing of multiple single units responding
simultaneously to a stimulus. Therefore, in order to understand the
underlying principles of the neural code it is imperative to characterize
the correlations between neurons and the impact that these correlations have
on the amount of information encoded by populations of neurons. We use
chronically implanted tetrode arrays to record simultaneously from many
neurons in the primary visual cortex (V1) of awake, behaving macaques. We
find that the correlations in the trial-to-trial fluctuations of their
firing rates between neurons under the same stimulation conditions (noise
correlations) in V1 were very small (around 0.01 in 500 ms bin window)
during passive viewing of sinusoidal grating stimuli. We are also measuring
correlations in extrastriate visual areas and investigating the impact of
correlations on encoding stimulus uncertainty by neuronal populations, under
different stimulus and behavioral conditions.