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The Journal of Neuroscience, April 1, 2002, 22(7):2956-2962
Completing the Corticofugal Loop: A Visual Role for the
Corticogeniculate Type 1 Metabotropic Glutamate Receptor
Casto
Rivadulla,
Luis M.
Martínez,
Carmen
Varela, and
Javier
Cudeiro
Neuroscience and Motor Control Group (NEUROcom), Facultad de
Ciencias de la Salud (Departamento de Medicina) and Instituto
Nacional de Educacion Fisica de Galicia, Campus de Oza, 15006 A
Coruña, Spain
The way in which the brain deals with sensory information relies
not only on feedforward processing of signals from the periphery but
also on feedback inputs. This is the case of the massive projection back from layer 6 in the visual cortex to the thalamus, for which, despite being the greatest single source of synaptic contacts, the
functional role still remains unclear. In the cat lateral geniculate
nucleus, part of this cortical feedback is mediated by type 1 metabotropic glutamate receptors (mGluR1s), which are exclusively
located on distal segments of the relay-cell dendrites. Here we show
that in adult cats the cortex uses a synaptic drive mediated by these
receptors (mGluR1) specifically to enhance the excitatory center
of the thalamic receptive field. Moreover the effect is maximum in
response to those stimuli that effectively drive cortical cells, and
importantly, it does not affect the spatiotemporal structure of the
thalamic receptive field. Therefore, cortex, by closing this
corticofugal "loop," is able to increase the gain of its thalamic
input within a focal spatial window, selecting key features of the
incoming signal.
Key words:
LGN; visual cortex; corticothalamic; metabotropic
receptors; feedback modulation; layer 6
Copyright © 2002 Society for Neuroscience 0270-6474/02/2272956-07$05.00/0
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