We examined how the depression of intracortical inhibition due to a reduction in ambient GABA concentration impairs perceptual information processing in schizophrenia. A neural network model with a gliotransmission-mediated ambient GABA regulatory mechanism was simulated. In the network, interneuron to glial cell and principal cell to glial cell synaptic contacts were made. The former hyperpolarized glial cells and let their transporters import (remove) GABA from extracellular space, thereby lowering ambient GABA concentration, reducing extrasynaptic GABAa receptor-mediated tonic inhibitory current and thus exciting principal cells. In contrast, the latter depolarized glial cells and let the transporters export GABA into the extracellular space, thereby elevating ambient GABA concentration and thus inhibiting principal cells. A reduction in ambient GABA is assumed in a schizophrenia network. Multiple dynamic cell assemblies were organized as sensory feature columns. Each cell assembly responded to a sensory feature stimulus. Tuning performance of the network to a feature stimulus was evaluated in relation to the level of ambient GABA. Transporter-deficient glial cells caused a deficit in the GABAergic gliotransmission and reduced ambient GABA concentration, which markedly deteriorated the tuning performance of the network, broadening the sensory tuning. Interestingly, the GABAergic gliotransmission mechanism could regulate local ambient GABA levels. Namely, it augmented ambient GABA around stimulus-irrelevant principal cells, while reducing ambient GABA around stimulus-relevant principal cells, thereby ensuring their selective responsiveness to the applied stimulus. We suggest that a deficit in GABAergic gliotransmission may cause a reduction in ambient GABA concentration, leading to a broadening of sensory tuning in schizophrenia. The GABAergic gliotransmission mechanism, proposed here, may have an important role in the regulation of local ambient GABA levels, thereby improving the sensory tuning performance of the cortex.
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