Talks and Conference Presentations

Computational Neuroscience
10th Annual Meeting
June 30-July 5, 2001
San Francisco and Pacific Grove, California

• Category-Specific Excitatory and Inhibitory Processes in Human Extrastriate Cortex
  Truett Allison¹, Aina Puce², and Gregory McCarthy^{3
  1}Department of Neurology, Yale University School of Medicine; ²Brain Sciences Institute, Swinburne University of Technology; ³Brain Imaging and Analysis Center, Duke University Medical Center

  Single-cell recordings from the temporal lobe of monkeys viewing stimuli show that cells may be highly selective, responding for example to particular complex non-objects (e.g. Fujita et al., 1992) or to objects such as faces (e.g. Perrett et al., 1992). However, stimulus-selective cells may be inhibited by non-preferred stimuli (e.g. Perrett et al., 1991). Can such inhibitory "sharpening" mechanisms be detected in human visual cortex? The fusiform gyrus generates N200 ERPs to specific categories of stimuli such as faces and words (e.g. Allison et al., 1999). Laminar recordings and CSD analysis in animal cortex (e.g. Mehta et al., 2000) suggest that the human N200 reflects excitatory depolarizing potentials in apical dendrites of pyramidal cells. We found that 26% of face-specific N200 sites generate a P200 ERP to words. Conversely, 56% of word-specific sites generate P200s to faces. P200 likely reflects hyperpolarizing inhibition of apical dendrites.

  These results suggest that: cells responsive to one stmulus category inhibit cells responsive to another category; inhibition of word-specific cells by faces appears to be stronger than the converse; inhibition also requires energy, hence it is likely that fMRI studies of face and word processing activate areas involved both in "center" excitation and "surround" inhibition.

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