Global and fine information coded by single neurons in the temporal visualcortex

When we see a person's face, we can easily recognize their species, individ ual identity and emotional state. How does the brain represent such complex information? A substantial number of neurons in the macaque temporal corte x respond to faces(1-12) However, the neuronal mechanisms underlying the pr ocessing of complex information are not yet clear. Here we recorded the act ivity of single neurons in the temporal cortex of macaque monkeys while pre senting visual stimuli consisting of geometric shapes, and monkey and human faces with various expressions. Information theory was used to investigate how well the neuronal responses could categorize the stimuli. We found tha t single neurons conveyed two different scales of facial information in the ir firing patterns, starting at different latencies. Global information, ca tegorizing stimuli as monkey faces, human faces or shapes, was conveyed in the earliest part of the responses. Fine information about identity or expr ession was conveyed later, beginning on average 51 ms after global informat ion. We speculate that global information could be used as a 'header' to pr epare destination areas for receiving more detailed information.