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PS3019 Cognitive and Clinical Neuropsychology “What” and “Where” systems in the cortex Lectures 5 & 6 Modularity in the visual pathways Superior longitudinal fasciculus Reading - Goodale, M.A. & Milner, A.D. (2004). Sight Unseen. Oxford, Oxford University Press. Chapter 4 and 5. - Milner, A.D. & Goodale, M.A. (1995). The visual brain in action. Oxford, Oxford University Press. Chapter 1, 2 &3. Inferior longitudinal fasciculus Additional reading Kolb, B & Whishaw, I.Q. (2003), Fundamentals of Human Neuropsychology, New York, Worth (5th ed). Chapter 8 pp. 180-183, Chapter 13, Chapter 15, pp. 382-384 Primary visual pathways Frontal eye fields (7) (voluntary eye movements) Pre-tectum (2) (pupil size in response to light intensity) Superior colliculus (head orientation and eye movements) Visual cortex Visual pathways cortical and sub-cortical functions Traditional approaches to vision in animals and humans the type of motor response is irrelevant animal discrimination learning human psychophysics Schneider (1969) Task 1 Position of reward left right Impaired by lesions of superior colliculus Task2 Visual discrimination Impaired by lesions of visual cortex Different motor responses required in an operant chamber, jumping stand or WGTA The common assumption is that any response can equally be selected on the basis of task requirements and internal representations of the visual stimuli Preferential access of specific motor output to specific visual input not considered 1 Rewired frogs (Ingle 1973, 1980, 1991) Unilateral removal of tectum Projections from retina to intact (ipsilateral) tectum Visuo-motor control in water beetles (Shone, 1962) Larvae will swim towards light if in need of air and away from light when air supply has been replenished no need for internal representation reflexes can be flexibly modulated by internal drive Similar control of behaviour in single-cell organisms (e.g. Euglena) reinforce the notion of non-representational visuo-motor reflexes preys Mirror symmetrical responses to: What does a rewired frog “see”? looming disk Has the evolution of more sophisticated visual systems in mammals resulted in a radical re-organisation of the visual brain? Unaffected obstacle avoidance pre-tectal function 0 0 0 45 45 45 90 90 90 Rewiring of pre-tectal nuclei produces opposite pattern of results Ellard and Goodale, 1986 Visuo-motor modules in mammals - mostly ignored - at sub-cortical level similar to amphibia superior colliculus (equivalent of frog’s tectum) fibres to controlateral brain stem visual “grasp” reflex elicited by stimulation eye movements in primates foveal vision orienting responses in rodents feeding, predation? fibres to ipsilateral brain stem escape responses Ipsilateral fibres from SC to brain stem – escape response to black rectangular target introduced in visual field Micro-stimulation of superior colliculus in Mongolian gerbil A) Orienting response B) Escape response SH Sham Operation Smooth head and body turns in direction opposite of that of electrical stimulation Rapid running movements in direction ipsilateral to the stimulation site (and with little head turning) D lesion of controlateral fibres from Superior Colliculus LT lesion of ipsilateral fibres from Superior Colliculus SC lesion of Superior Colliculus itself 2 Pretectal Nuclei barrier avoidance Primate superior colliculus preserved archaic circuit regulation of involuntary eye movements Evolution of complex forms of visuo-motor control SH Sham Operation e.g. required by emergence of prehensile hand expansion of visuo-motor systems in the cortex SC1 & SC2 Lesion of Superior Colliculus PT Lesion of Pretectal Nuclei VC Lesion of Visual cortex Lesion studies in monkeys 1860s Ferrier lesions of (what we now call) dorsal system mis-reach for food items Murata et al. (2000) Neurons of front end of parietal cortex respond when monkey looks at and grasps specific types of solid shapes 1980s Glickstein et al. lesions of dorsal stream inability to reach for food in slots of different orientation Electrophysiological studies in monkeys 1970s Mountcastle & Hyvarinen electrophysiological recordings from dorsal stream neurons neurons that fire during reaching neurons firing during saccades towards stationary objects neurons responding to moving objects if followed by gaze Visuo-motor control in humans In both humans and non-human primates: The visual brain areas of monkeys and humans are remarkably similar the coordination of saccadic movements, pursuit eye movements, grasping with the hand and body locomotion is computationally complex if carried out by a single central system - As such different specialised circuits may have evolved with a certain degree of autonomy - There is evidence for separate modules in posterior parietal cortex and circuits linking the parietal cortex with the pre-frontal cortex and non-cortical archaic structures such as the superior colliculus and the cerebellum 3 Modularity in the parietal cortex fMRI studies in humans reveal similar functions (Culham et al., 2003; 2004) Activity in Lateral Intraparietal area traditionally attributed to shifts of attention and updating of spatial information Snyder Batista & Andersen (1997) monkeys trained (conditional response to colour cue) to respond to the same stimuli with different responses double dissociation LIP activated by eye movements PPR activated by arm movements response requirements are just as important as shifts of spatial attention Blindsight Cortical blindness in neuropsychological patients Damage to V1 causing blindness in corresponding portion of visual field Scotoma blind regions of visual field Monkeys with V1 removed (Gross, 1973) no discrimination of visual patterns no activity in ventral stream Weiskrantz et al. (1974); Weiskrantz (1986) residual ability to detect items of food and reach for them residual ability to guess locations in patients with cortical blindness Left visual cortex Typically assessed by perceptual report e.g. Can you see this light? Weiskrantz et al. (1974); Perry and Cowey (1984) visual ability in “blindsight” attributed to functions of superior colliculus Area of impaired vision However, more sophisticated residual perceptual abilities unlikely to be mediated by subcorical structures Natural blind spot Weiskrantz et al., (1974; 1986; 1987) - Patient D.B. (hemianopia) - Unable to report light in blind visual field - Correlation of saccade position to “guessed” target positions within blind visual field - High correlation of pointing and guessed target positions - No evidence of systematic response location in control trials with no taget or target presented in blind spot Perenin & Rossetti (1993) some patients can scale grip and rotate wrist when reaching for objects in blind field Accuracy and latency of blindsight affected by nature of response (e.g. Marcel 1993; Zihl & von Cramon 1980) verbal (more arbitrary?) poor performance and long latency blinks, finger movements (less arbitrary?) faster and more accurate response 4 Evidence of modularisation in the ventral stream? Some high level cells will respond to particular stimuli irrespective of variations in size, orientation, colour, luminosity etc. Specialised cells and brain areas for recognition of specific category of objects (as reviewed in Lectures 1&2) e.g. face cells in the ventral stream e.g. Perrett et al. (1984; 1991) cells in Superior Temporal Sulcus category specific (e.g. faces) some are “object centred” useful for object recognition For very salient and biological important categories of objects such as faces, there may be specialised high order cells For other objects it is likely that specialisation and categorisation is supported by the columnar organisation of cells sensitive to similar features Tanaka and colleagues (1991; 1992; 1994) cells with similar but slightly different selectivity cluster in columns in the Inferior Temporal cortex stimulus equivalence is obtained at the column level fMRI evidence for specialised modules on the ventral system Fusiform Face Area (FFA) activated by faces not by objects, buildings or scrambled faces Parahippocampal Place Area (PPA) activated by pictures of buildings and scenes not by faces Lateral Occipital area (LO) activated by common objects not by faces or buildings Clinical evidence of modularity in the ventral system although often overlapping, prosopagnosia and agnosia for objects can dissociate case C.K. agnosia for objects but not for faces Summary Visuo-motor modules in lower vertebrates Visuo-motor modules in mammals? Blindsight “topographical agnosia” inability to navigate in familiar environment (e.g. home town) loss of recognition of landmarks can dissociate from other forms of agnosia Evidence for modularity in the dorsal system Evidence for modularity in the ventral system 5