CNTRICS April 2010

Center-surround:Adaptation to context in

perception

Robert ShapleyCenter for Neural ScienceNew York University

Perceptual adaptation --what it may tell us about cortical circuitry in schizophrenia

• Adaptation is a fundamental aspect of brain activity• Center-surround interaction is a kind of adaptation• Behavioral evidence for center-surround malfunction

in schizophrenic patients• Mechanisms suggested by primate neurophysiology

• Local Field Potential (LFP) power in the gamma band• Gamma and center-surround mechanisms• Implications of gamma abnormalities

Center-surround perceptual effects and schizophrenia

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Dakin et al Current Biology 2005

Adaptation: a fundamental aspect of brain activity

“We conclude, therefore, that sense organs are not rigid machines but living and variable systems, the functioning of which is subject to variation. If a sensory system is exposed to a new and prolonged stimulus situation that departs from the one normally experienced, the system can be expected to undergo a fundamental change in its normal mode of operation.” (Ivo Kohler, 1962)--[my underlining]

V1 cortex in monkey and human

Intracolumnar feedforward and feedback connections (Sincich & Horton) Note LOOPS!

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Size tuning in V1 receptive fields:evidence for center-surround

Cortical receptive field as a difference of gaussians

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Suppression indexSI= Kib2/Kea2

There is a lot of surround inhibition in V1(SI=inh/exc)

maximal in layer 4B

Collinear and Orthogonal Suppression: collinearmuch stronger because of tuned suppression

Local Field Potential (LFP)fluctuations

and center-surround interactionThe Local Field Potential reflects the activity of many neurons in the local region around the electrode.

Peaks in the power spectrum of the LFP may be clues to the properties of the cortical network (and its malfunctions). In V1 cortex the gamma band, defined as the band 25-90 Hz, is very useful.

V1 cortex--responses to drifting grating patterns

Gamma band peaks evoked by visual stimulation in V1

Gamma Band peaks in LFP spectrum grow with stimulus size

Cortical resonance model of gamma-band peaks(Kang, Shapley, Henrie, Shelley, 2009)

Implications of gamma abnormalities in schizophrenia

•Change in E/I balance in the local circuit•Hypothesis --reduced local circuit inhibition caused by something wrong in GABA inhibitory neurons or synapses•Consistent with NMDA-->GABA malfunction leading to weakened GABA signal

from Lisman et al (2005) TINS 31, 234-242

Similarities to the ideas in the Lisman hippocampus model

Perceptual adaptation --what it may tell us about cortical circuitry in schizophrenia

• Adaptation is a fundamental aspect of brain activity• Center-surround interaction is a kind of adaptation• Behavioral evidence for center-surround malfunction in

schizophrenic patients• Mechanisms suggested by primate neurophysiology

• Local Field Potential (LFP) power in the gamma band• Gamma and center-surround mechanisms• Implications of gamma abnormalities