SOKENDAI physiology lecture course 2013"Neuroscience of Cognition and Motor control" #8"Neural Mechanism of Blindsight"June 14, Friday 10:00-12:00, Myodaiji Staff Hall 2F Meeting roomMasatoshi Yoshida (NIPS and SOKENDAI, Assistant professor)1. What is Blindsight (盲視)?Q: What is blindsight?• A: “The visually evoked voluntary responses ofpatients with striate cortical destruction thatare demonstrated despite a phenomenalblindness” 1• Phenomenal consciousness can bedissociated from visual information processing.2. Two visual systems:Cortical vs. Subcortical2-1. Two visual systems in monkeys• Bilateral lesion in V1 - first report of blindsightin monkey 2• Retained: visually guided reaching andobstacle avoidance 32-2. Two visual systems in rodents• Double dissociation - lesion in visual cortexand in the superior colliculus 4• SC for orienting 5• Visual cortex for pattern discrimination 62-3. Two visual systems in frogs• Two Visual Systems in the Frog 7• Lesion in the optic tectum induces rewiring.• Neocortex for obstacle avoidance• Optic tectum for Response to preys3. Two cortical visual systems:Dorsal vs. Ventral3-1. What and where pathways (Mishkin &Ungerleider)• The neurons in the dorsal pathway areselective to motion and binocular disparity.• The neurons in the ventral pathway areselective to shape and color. 8• Bilateral removal of area TE: Objectdiscrimination - Which is the unfamiliar object?• Bilateral removal of posterior parietal cortex:Landmark discrimination:• Which is near to the landmark? 93-2. Vision for perception and vision foraction (Goodale and Milner)• Dorsal pathway: Vision for action -unconscious• Ventral pathway: Vision for perception –conscious 10• Optic ataxia (視覚性運動失調)• Damage in the posterior parietal cortex -supramarginal gyrus and angular gyrus• Orientation error does not depends on handbut on visual field.• Damage in the dorsal pathway affects visionfor action. 11• Visual form agnosia (視覚失認):• Subject DF: Bilateral damage in ventral visualpathway (Lateral occipital area: LO)• Very good performance in ‘posting’ task 12• DF matched her card orientation to the slotduring the course of the movement, well beforecontacting the target. 13• Functional double dissociation• "Visual phenomenology ... can arise only fromprocessing in the ventral stream ..." "visual-processing modules in the dorsalstream ... are not normally available toawareness." ("The visual brain in action"p.200-201)14
3-3. Perceptual experience in visual agnosia• Retained color, texture perception• Degraded form perception• a piece of kitchen equipment” it’s got a redpart to it, a red handle” it goes down into asilver corrugated part” the red part’s plasticand the other part’s metal.” (When she washanded it) “Oh, it’s a torch.” 15• She has difficulty describing her visualexperience, only saying that objects tend toappear ‘blurred’ and that separate elements‘run into each other’. 13• Yoshidas comment: She experiences color,texture and motion of small elements. This isthe biggest difference from the experience ofblindsight. This is the strongest evidence thatV1, not the ventral pathway, is necessary forconscious experience.3-4. Are they really independent?• Single-line copying task• She draw ‘in the air’ before copying (1st trial).• She imagined herself tracing on top of the lineand translate the image into drawing. It takes alonger time (5-10sec).• DF developed a strategy to overcomeperceptual deficit by visuomotor skills. 16• Lesson learned: Perceptual task can be solvedby visuomotor skill.• It is very important to control tasks not todevelop unexpected strategy.4. Blindsight in human4-1. Case reports• G.Y. became blind in his right visual field dueto traffic accident in eight years old. He wasdiagnosed as homonymous hemianopia.• Above-chance performance in forced-choice=> blindsight 17• A blindsight subject in Japan4-2. Relationship between Blindsight andtwo-visual systems hypothesis• Access to the dorsal pathway in blindsight4-3. Affective blindsight• Discrimination of Emotion of face (Fearfull vs.happy) <==> Discrimination of identity of faces18• Alarm system in subcortical pathway 19• Subcortical face processing 204-4. Plasticity in blindsight• 2-3 months training is necessary for blindsight.21• DTI revealed crossed connection betweenLGN and MT. 22• DTI revealed stronger connection SC ->Pulvinar -> Amygdala 235. Blindsight in monkey5-1. Blindsight in monkeys• Blindsight after 2-3 months training 24• Are the monkeys really ‘blind’ to the visualstimuli? The monkeys behaved as if it is aNo-target trial. The monkeys are ‘not able tosee’, as in human blindsight.5-2. Neural circuit for blindsight• Blindsight disappear after SC inactivation. 25• MT response does not disappear after V1lesion.• MT response disappear after additional lesionof SC. 26,27• Inactivation of LGN abolishes blindsight 28• They did not inactivate the SC. Thus they didnot reject possibility that blindsight dependsboth on LGN and SC.• Inactivation of the SGS abolishes blindsight. 296. SummaryThe idea of two visual systems (cortical vs.subcortical) was confirmed in various animals.1. Dorsal and ventral visual pathways mayhave different roles on unconscious andconscious vision, or vision for action andvision for perception.2. Controversy over the neural circuit forblindsight is not settled.
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