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Synaptic basis for intense thalamocortical activation of feedforward inhibitory cells in neocortex

Summary: Synaptic basis for intense thalamocortical activation
of feedforward inhibitory cells in neocortex
Scott J Cruikshank1, Timothy J Lewis2 & Barry W Connors1
The thalamus provides fundamental input to the neocortex. This input activates inhibitory interneurons more strongly than
excitatory neurons, triggering powerful feedforward inhibition. We studied the mechanisms of this selective neuronal activation
using a mouse somatosensory thalamocortical preparation. Notably, the greater responsiveness of inhibitory interneurons was not
caused by their distinctive intrinsic properties but was instead produced by synaptic mechanisms. Axons from the thalamus made
stronger and more frequent excitatory connections onto inhibitory interneurons than onto excitatory cells. Furthermore, circuit
dynamics allowed feedforward inhibition to suppress responses in excitatory cells more effectively than in interneurons.
Thalamocortical excitatory currents rose quickly in interneurons, allowing them to fire action potentials before significant
feedforward inhibition emerged. In contrast, thalamocortical excitatory currents rose slowly in excitatory cells, overlapping with
feedforward inhibitory currents that suppress action potentials. These results demonstrate the importance of selective synaptic
targeting and precise timing in the initial stages of neocortical processing.
The neocortex, which comprises the majority of the mammalian brain,
is critical for sensation, perception, goal-directed behavior and cogni-
tion1. It contains two general classes of neurons: excitatory cells that
release the neurotransmitter glutamate and inhibitory interneurons
that release the neurotransmitter GABA. Subsets of both types of cells
are directly innervated by excitatory thalamic relay neurons, which are
the main source of extrinsic input to the neocortex. Curiously,


Source: Andrzejak, Ralph Gregor - Departament de Tecnologia, Universitat Pompeu Fabra
Lewis, Tim - Department of Mathematics, University of California, Davis


Collections: Biology and Medicine; Computer Technologies and Information Sciences