Blindsight relies on a functional connection between hMT+ and the lateral geniculate nucleus, not the pulvinar

Abstract

When the primary visual cortex (V1) is damaged, the principal visual pathway is lost, causing a loss of vision in the opposite visual field. While conscious vision is impaired, patients can still respond to certain images; this is known as ‘blindsight’. Recently, a direct anatomical connection between the lateral geniculate nucleus (LGN) and human motion area hMT+ has been implicated in blindsight. However, a functional connection between these structures has not been demonstrated. We quantified functional MRI responses to motion in 14 patients with unilateral V1 damage (with and without blindsight). Patients with blindsight showed significant activity and a preserved sensitivity to speed in motion area hMT+, which was absent in patients without blindsight. We then compared functional connectivity between motion area hMT+ and a number of structures implicated in blindsight, including the ventral pulvinar. Only patients with blindsight showed an intact functional connection with the LGN but not the other structures, supporting a specific functional role for the LGN in blindsight.

Extrastriate connectivity of the mouse dorsal lateral geniculate thalamic nucleus

“…LGd inactivation in VISp lesioned mice has been shown to reduce extrastriate activity and eliminate blindsight behavior (Schmid et al, ). Human imaging studies have suggested that LGd projections to extrastriate area MT are the critical anatomical substrate to blindsight (Ajina et al, ; Ajina & Bridge, ; Sincich et al, ). Area MT in humans (also known as V5 in primates) is part of the dorsal visual‐processing stream and plays an important role in motion perception as MT neurons are tuned to the speed and direction of moving visual stimuli (Born & Bradley, ).…”

The influence of subcortical shortcuts on disordered sensory and cognitive processing

“…In support of a role for the LGN, there are reports of enhanced structural connectivity 180 and functional connectivity 181 between the LGN and V5 in patients who are cortically blind who have motion-related blindsight, whereas connectivity between the pulvinar and V5 is the same irrespective of whether or not a patient has blindsight 181 . Furthermore, residual neurons within the macaque LGN (which becomes profoundly degenerated after V1 lesions) transmit visual information to V5 that support preserved visual abilities 92 , regardless of in which life stage a V1 lesion is incurred 165 .…”

The Superior Colliculus and Amygdala Support Evaluation of Face Trait in Blindsight

“…We also anticipate that blindsight function will depend upon the underlying visual structures. Therefore, patients demonstrating blindsight for trustworthiness and dominance traits here may not necessarily have shown motion blindsight on previous studies and vice versa (13)(14)(15). This has potential implications for clinical practice, as blindsight may offer a mechanism for training and rehabilitation after V1 damage.…”

“…This was defined as achieving either an average score, or a score for individual conditions that was significantly above chance, using a statistical threshold of p < 0.05 and a cumulative binomial distribution. This was an identical method to our previous work, except that the stimulus was a face rather than a drifting Gabor (15) or moving dots (13). The critical point was that patients performed above chance despite absent visual capacity in the targeted region of the visual field according to Perimetry (Figure 1).…”