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nature neuroscience volume 2 no 3 march 1999 277 Although retinal input relayed through the lateral geniculate
 

Summary: nature neuroscience volume 2 no 3 march 1999 277
Although retinal input relayed through the lateral geniculate
nucleus (LGN) of the thalamus clearly drives responses in the
primary visual cortex (V1), LGN afferents account for only a
small fraction of the synapses onto V1 neurons17. The primary
source of synaptic input to neurons in primary visual cortex, at
least in terms of numbers, is excitatory input from other nearby
cortical neurons. What role do these local recurrent connections
have in shaping the responses of V1 neurons to visual stimuli?
One interesting idea is that recurrent connections amplify weak
feedforward input signals from the LGN8 and increase neuronal
selectivity811. Neurons in the primary visual cortex are selective
for a number of stimulus characteristics, including the orientation
and direction of motion of light bars or gratings. Previous stud-
ies have suggested that cortical amplification may enhance ori-
entation tuning911 or direction selectivity8. Experiments in which
cortical connections are disrupted by cooling or shocking the
cortex suggest that recurrent connections do indeed amplify input
signals, but they do not support the idea that this cortical ampli-
fication increases orientation or direction selectivity12,13. Thus,

  

Source: Abbott, Laurence - Center for Neurobiology and Behavior & Department of Physiology and Cellular Biophysics, Columbia University

 

Collections: Biology and Medicine