Spatial Attention Weakly Modulates Visual Responses in the Lateral Geniculate Nucleus.

Visual responses in the cortex are strongly influenced by shifts in spatial attention. This modulation of visual processing includes changes in firing rate, decreased response variability, and decreased interneuronal correlations; all of which are thought to underlie enhanced perception near the center of attention at the cost of perception at other locations. Information from the retina is relayed to primary visual cortex via neurons in the lateral geniculate nucleus (LGN) of the thalamus. Although early studies describe an enhancement of LGN activity with spatial attention, more recent work has cast doubt on this view. Given its strategic position as the gateway to the cortex, an understanding of the effects of attention on visual processing in the LGN is important. We therefore performed experiments to reexamine the influence of spatial attention on spiking activity in macaque LGN (one male, one female) and applied a broad set of analyses and functional metrics to assess possible effects. Our results reveal a statistically significant effect of spatial attention in the LGN: firing rates were slightly higher and more reliable when monkeys directed attention toward the receptive fields of recorded neurons compared with when attention was directed to different retinotopic locations. However, effects were much smaller than previously reported (∼1 vs ∼4%) and further analyses suggest that effects are weak, inconsistent, and restricted to a small subset of parvocellular and magnocellular neurons. Thus, while spatial attention does exert an influence in the LGN, its effects are weak and may have limited impact on downstream processing.