Dataset Information

GABA, noise and gain in human visual cortex.

ABSTRACT: High levels of GABA (gamma-aminobutyric acid, the brain's primary inhibitory neurotransmitter) are associated with enhanced cognitive and perceptual performance. It has been proposed that these effects result from GABA reducing neural noise or variability, but the precise mechanisms remain unknown. We have measured how individual differences in GABA concentration in the visual cortex are related to performance on a visual contrast discrimination task. Our results reveal that the facilitatory strength of the typical "dipper" function elicited by this task is strongly correlated with GABA concentration. A simple, biologically plausible, network model comprising excitatory and suppressive neural populations accounts for the data well and indicates that the strength of suppression increases as GABA concentration increases. Inter-individual variations in GABA were correlated both with the inhibition strength of the model (mimicking the effect of GABA) and, inversely, with the magnitude of the response criterion. This enhanced suppression has the dual effect of suppressing noise and reducing the gain of the neural response. Our findings thus suggest that the changes in performance conferred by high GABA concentration are mediated by both a reduction of noise and, paradoxically, a reduction in neural, but not perceptual, sensitivity.

SUBMITTER: Hammett ST

PROVIDER: S-EPMC7511597 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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GABA, noise and gain in human visual cortex.

Hammett Stephen T ST Cook Emily E Hassan Omar O Hughes Ceri-Ann CA Rooslien Hanna H Tizkar Rana R Larsson Jonas J

Neuroscience letters 20200807

High levels of GABA (gamma-aminobutyric acid, the brain's primary inhibitory neurotransmitter) are associated with enhanced cognitive and perceptual performance. It has been proposed that these effects result from GABA reducing neural noise or variability, but the precise mechanisms remain unknown. We have measured how individual differences in GABA concentration in the visual cortex are related to performance on a visual contrast discrimination task. Our results reveal that the facilitatory str ...[more]

PMID: 32777347

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Project description:BackgroundPrevious reports of inhibition in the neocortex suggest that inhibition is mediated predominantly through GABA(A) receptors exhibiting fast kinetics. Within the hippocampus, it has been shown that GABA(A) responses can take the form of either fast or slow response kinetics. Our findings indicate, for the first time, that the neocortex displays synaptic responses with slow GABA(A) receptor mediated inhibitory postsynaptic currents (IPSCs). These IPSCs are kinetically and pharmacologically similar to responses found in the hippocampus, although the anatomical specificity of evoked responses is unique from hippocampus. Spontaneous slow GABA(A) IPSCs were recorded from both pyramidal and inhibitory neurons in rat visual cortex.ResultsGABA(A) slow IPSCs were significantly different from fast responses with respect to rise times and decay time constants, but not amplitudes. Spontaneously occurring GABA(A) slow IPSCs were nearly 100 times less frequent than fast sIPSCs and both were completely abolished by the chloride channel blocker, picrotoxin. The GABA(A) subunit-specific antagonist, furosemide, depressed spontaneous and evoked GABA(A) fast IPSCs, but not slow GABA(A)-mediated IPSCs. Anatomical specificity was evident using minimal stimulation: IPSCs with slow kinetics were evoked predominantly through stimulation of layer 1/2 apical dendritic zones of layer 4 pyramidal neurons and across their basal dendrites, while GABA(A) fast IPSCs were evoked through stimulation throughout the dendritic arborization. Many evoked IPSCs were also composed of a combination of fast and slow IPSC components.ConclusionGABA(A) slow IPSCs displayed durations that were approximately 4 fold longer than typical GABA(A)fast IPSCs, but shorter than GABA(B)-mediated inhibition. The anatomical and pharmacological specificity of evoked slow IPSCs suggests a unique origin of synaptic input. Incorporating GABA(A) slow IPSCs into computational models of cortical function will help improve our understanding of cortical information processing.

Dataset Information

GABA, noise and gain in human visual cortex.

Publications

GABA, noise and gain in human visual cortex.

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