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

Visual responses in the cerebral 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 visual perception near the center of attention at the cost of visual perception at other locations. Visual information from the retina is relayed to primary visual cortex via neurons in the lateral geniculate nucleus (LGN) of the dorsal 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 covert spatial attention on the spiking activity of single units in the macaque LGN 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 towards the receptive fields of recorded neurons compared to 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 and inconsistent. Thus, while spatial attention does exert an influence in the LGN, its effects are weak and may have limited impact on downstream processing. Significance Statement: The lateral geniculate nucleus (LGN) is a critical relay in the visual system, shaping the flow of sensory information from the eye to the brain. Although higher-order brain regions show strong modulation by attention, it remains unclear whether the LGN is similarly affected. By directly recording LGN activity in monkeys performing a covert attention task, we found that spatial attention produces only weak and inconsistent modulation of visual responses. These findings suggest that the LGN largely operates independently of spatial attention, highlighting a potential boundary between early sensory processing and cognitive control.