Pulvinar Pathway Flashcards
What processing idea is put forward by Le Doux et al?
Notion of a separate subcortical route for visual perception of complex form
What is blindsight?
The ability to make visual discriminations in the absence of awareness associated with damage to visual cortex
How did Riddoch study blindsight?
Individuals with visual cortex lesion caused by gunshot wounds that were nevertheless able to perceive motion within the damaged area
What study looks at blindsight for facial expressions?
De Gelder et al, presented 4 movies showing happy, sad, angry or fearful facial expressions
What do fMRIs show for affective blindsight?
Morris et al 2001 and patient GY. Faces presented to blind hemifield didn’t not evoke increased response in visual cortex, but response to unseen fear in amygdala, which correlated with pulvinar and SC response. This is suggestive of pulvinar pathway
What is the background research for the pulvinar pathway?
Search tasks (parallel processing of threat), visual processing in animals without visual cortex, innate stimulus processing
How does Hansen and Hansen’s study show evidence for the fast pulvinar route?
Threatening faces jump out of crowds, perhaps as a result of a pre-attentive, parallel search for signs of threat (though this has not always been replicated, and these results were likely due to the stimulus)
How do frogs demonstrate threat detection?
No visual cortex but have prey response to small objects and threat response to large objects. Mediated by structures analogous to thalamus and superior colliculus (Ewert et al 2001)
What are some issues with the pulvinar pathway?
Few individuals have ‘emotional blindsight’ (case study problems and islands of sparing). Low temporal resolution of fMRI (MEG is a high temporal alternative but noisy)
What do single-cell recordings show about whether the subcortical route is actually faster?
Subcortical is not faster than cortical processing. Crucial variable is time at which reliable differences between affective and non-affective stimuli can be detected (Pessoa and Adolphs 2010)
How does connectivity differ in the pulvinar pathway?
Usual route is retina to LGN to V1 etc. Pulvinar route is retina to SC to pulvinar to amygdala
What is the superior colliculus>
Able to deal with complex visual stimuli. Dependent on higher visual areas. Superficial areas retinotopically mapped. Greater depth organisation becomes less distinct. Deep areas are polysensory (reactive to visual, auditory and tactile stimuli and possibly encode more abstract perceptual decisions)
What are the effects of ablation on visual discrimination?
Discriminative pulvinar responses to complex visual form are destroyed when visual cortex is ablated but not when SC is ablated
What are the two separate circuits of the medial pulvinar?
Central/lateral MP and the medial MP. If the SC connections to amygdala via pulvinar were significant, they would be expected to share the same circuit but they don’t
What do connectivity and lesions studies suggest about the SC and pulvinar?
Suggest the SC and pulvinar are not optimised for the processing of visual form, including complex form like facial expressions
