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Henry J. Alitto, W. Martin Usrey; Spatial attention and visual processing in the lateral geniculate nucleus. Journal of Vision 2008;8(17):3. doi: 10.1167/8.17.3.
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Several studies have shown that spatial attention increases the responsiveness of neurons throughout striate and extrastriate cortical areas. Given the robust feedback pathway from striate cortex to the lateral geniculate nucleus (LGN) of the thalamus, it is possible that the cortical effects of attention may influence visual processing in the LGN. Because corticogeniculate axons provide direct excitatory input as well as polysynaptic inhibitory input onto LGN neurons, the effects of attention could be complex. Indeed, fMRI studies report increased blood flow to the LGN with attention1, while 2-deoxy-glucose studies report decreased metabolic activity in the magnocellular layers of the LGN with attention2.
To study the effects of spatial attention on the spiking activity of neurons in the macaque LGN, we trained two animals to perform a spatial attention task. In this task, animals fixated on a central location while two sine-wave grating patches were presented peripherally. One grating was presented over the receptive field of a recorded LGN neuron, while the second grating was presented at a different location. Animals were instructed to attend to one or the other grating in block format based on the color of the fixation spot. At a random delay after the onset of fixation, the contrast of the attended grating either increased or decreased. Animals were rewarded for correctly reporting the nature of the contrast change. Catch trials demonstrate that animals were under proper behavioral control. Our results show that attention decreases the activity of magnocellular LGN neurons when distracter stimuli are located in the same visual hemifield as the receptive fields of recorded neurons, but not when the distracters are in the opposite visual hemifields. Given this result, we suggest an interaction between spatial attention and the extraclassical suppressive field of LGN neurons.
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VanduffelW.TootellR. B.OrbanG. A. (2000). Attention-dependent suppression of metabolic activity in the early stages of the macaque visual system. Cereb Cortex, 10, 109–126.
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