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Unilateral Neglect Overview ● Behavioural deficits observed in patients with unilateral neglect ● Contrast low-level (visual) and high-level (cognitive) explanations of neglect ● Describe behavioural dissociations observed in neglect ● Models of neglect ● Neglect not a unitary syndrome – can affect near space and/or far space – can be object-based and/or space-based – can influence perceptual processing and/or motor responses ● Attentional, Representational, Pre-motor ● May reflect damage to different brain circuits involved in representation of space and in orienting of attention The What and Where visual pathways (Ungerleider & Mishkin, 1982) ● What pathway (ventral stream - IT) - object recognition → Stored representations for our perceptual experience (PERCEPTION) ● Where pathway (dorsal stream - PPC) - spatial perception and action (eye movements, reaching and grasping) → The programming of our actions (ACTION) Evidence Landmark Task (Mishkin & Ungerleider, 1982) ● ‘What’ - Lesions in IT cortex produce deficits in shape discrimination tasks (Gross et al, 1973; Mishkin, 1982) ● ‘Where’ - Lesions in parietal cortex produce deficits in landmark task (Pohl et al., 1973) Patient D.F. (Goodale & Milner, 1992) ● Visual agnosia following carbon monoxide poisoning ● D.F. is unable to recognise objects e.g.g the man who mistook his wife for a hat ● Poor describing orientation of a slot ● But oriented hand correctly when posting a card in slot ● Action mediated by dorsal (How) pathway History

Clinical Neuropsychology ● WWI - Gordon Holmes (London); Walter Poppelreuter (Germany) ● WWII Joachim Bodamer (1947)

‘prosopagnosia’ (inability to recognise faces following bullet wound)

Russell Brain (1st Baron Brain)

Neglect, Pain, Visual Deficits

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Localisation of function from brain damage Psychologists increasingly interested in single case studies (1960’s -) Aim: make link between brain damage and behaviour Descriptions of deficits and localisation difficult 1970’s-90’s - Went beyond description of deficits and localisation Can learn about cognitive systems by studying how they breakdown after brain damage (Coltheart – Scholarpedia) ● Applications: Assessment and Rehabilitation

Cognitive Neuroscience - Biological substrates of cognition Unilateral Neglect ● Definition: Following right hemisphere brain damage a patient without impairment of intellectual functioning appears to ignore, forget or turn away from the left side of space- as if that half of the world has ceased to exist... Terminology ● Unilateral neglect is also called - Hemi-inattention - Visual neglect - Visual spatial neglect - Unilateral spatial neglect ● Other important terms - Contralesional (opposite side to brain damage) - Ipsilesional (same side as brain damage) - Hemianopia (a visual field defect) Classic cases of Neglect Brain (1941): 3 patients with right parieto-occipital damage - Case 5 ● When asked to describe how she would find her way from the tube station to her

flat, described in detail correctly and apparently visualising landmarks ● But consistently said right instead of left for the turnings except on one occasion Paterson and Zangwill (1944) Cases with missile wound in right parieto-occipital region (including angular gyrus) - will be in wheelchair bc they will bump into things Case 1 ● Patient often collided with objects on his left which though clearly perceived a few moments before ● Knocked over dishes on his left-hand side ● Occasionally missed food on the left-side of his plate. ● Will also show tactile neglect Case 2 (right parietal damage) ● Patient totally neglected his left upper extremity (of his own body) ● Despite good preservation of motor power Extinction ● Patients do not report left-hand stimulus when it is paired with a right-hand stimulus ● Sometimes described as mild form of neglect ● Others consider it a separate related disorder Everyday examples ● Patients may: - eat food from right side of plate only - dress only the right side of own body - shave the right side of their own face - deviate to right and may even go round in a circle - Note dense left hemiplegia Clinical tests ● Drawing – from memory – Copying ● Line bisection ● Cancellation tasks ● Reading – Single words - neglect dyslexia

Nature of brain damage associated with neglect ● Most commonly observed in humans following damage to the right hemisphere

(left neglect) ● Posterior parietal cortex (Specifically Inferior parietal lobe) - Brodmann's areas 39 and 40 (dorsal “where” visual pathway) - Left parietal damage rarely produces right sided neglect (and quickly recovers) ● Also some cases following sub-cortical damage – Thalamus, basal ganglia, white matter ● Right parietal cortex appears to play a dominant role in spatial cognition in humans

Functions of the Posterior Parietal Cortex (PPC) Visuo-motor control of behaviour (cant see objects if they overlap) Single cell recording shows these neurons involved in: ● Visually-guided reaching, Eye movements, Head (gaze) shims Effects of lesions to PPC in humans ● Misreaching (optic ataxia) ● Eye movement problems (fixed gaze)

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Constructional apraxia (difficulty putting things together) Simultanagnosia (inability to perceive more than one object at a time) Neglect (ignoring the left side of space) Can’t see objects if they overlap

Sensory explanations - Is neglect due to a visual field defect? e.g a left hemianopia

No because: ● Neglect has been observed for the left side of a mental image ● Some neglect patients do not have visual field deficits ● Patients can neglect the left side of individual objects presented in their intact right visual field ● Hemianopic patients (with damage to visual pathways and cortex) do not show neglect Neglect of a mental image – ‘Piazza del Duomo’ demonstration (Bisiach & Luzzatti, 1978) ● Two patients asked to describe a familiar scene (Cathedral Square in Milan) from memory ● Reported landmarks on right not those on left from both imaginary viewing positions

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Triangle = direction of (imaginary) view Black squares indicate buildings reported Could neglect reflect a failure to build a representation of the left side of space? Or of directing attention to a representation?

Unconscious, implicit processing in neglect ● What is the fate of the neglected stimuli? ● Are neglected stimuli processed outside of awareness? ● Normal cortically evoked potentials for neglected contralesional stimuli – Vallar et al. (1991) Residual processing of extinguished information ● Volpe et al. Nature, (1979) - Five patients with left extinction - Same/different judgments - Stimuli – LVF, RVF or both (150 ms)

Burning house study’ - Marshall & Halligan (1988) ● Single case study: Description implied houses were same - Which house would prefer to live in? Repeatedly chose non-burning house ● Two other reports of patients who chose burning house - Bisiach & Rusconi (1990) Dissociations and double dissociations ● Allow inferences about how cognitive system is organised ✖ based on dissociations ● Patient X impaired at reading but not at face recognition. ● Assertion is: reading and face ✓ recognition involve separate cognitive processes ● But it might be that argued that reading is harder than face recognition and Patient X is ✓ impaired on harder recognition tasks ● Double-dissociation - Patient Y – can read but can’t recognise faces → Separate systems for word recognition and face recognition

Dissociations in neglect ● Spatial versus object-based neglect ● For near or far space ● Perceptual or motor forms Spatial neglect ● Dissociation in eye movement behaviour ● Scenes chosen to guide (top- down) active search of left side ● Eye movement scanpath - Failure to scan left side of scene (spatial neglect) Karnath (1994) Spatial versus object-based neglect ● Some patients neglect left sides of objects but not the left side of space (scene) Gainotti, (1972) ● Case - RR → Walker et al. (1996) ● Object-based neglect influences pattern of eye movements ● Failure to scan left side of object not of scene

B.Q.’s Object-based neglect - Young et al. (1992) ● Patient B.Q. - Age 64 yrs, Right parietal lesion – persistent left neglect – Non hemianopic - Neglect for left-side of objects

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Chimaerics presented entirely in the right (intact) visual field - Digit report task Error rates: left 15/15 (none correct) Right 3/15 (80% correct)

● B.Q.’s lack of insight – when told both sides were different would maintain it was a single object ● B.Q’s finger tracing to illustrate picture was “a bowl” Pan (right), pig (left) “this must be the vegetables”

Object-based neglect ● B.Q.’s could be influenced by features on the left (tracing) and in responses: - Chimeric face Michael Parkinson/Terry Wogan “Terry Wogan , but there’s a touch of Picasso about him” ● B.Q. – can see features on left – finger tracing - May reflect normal perceptual process of Gestalt completion ● Deficient encoding left-sided information – Can be overcome when defining feature on left, or when chimaeric separated. Preserved object knowledge can interact with deficient left representation to aid recognition (B.Q. not susceptible to burning house task) Neglect dyslexia - Young et al. (1991) ● Patient SP’s single word reading errors occurred for words positioned anywhere on the page - left side of an object (object-based neglect) ● SP’s whole word omissions occurred only for words located on the left side of the page - left side of space (spatial neglect) - Related to defective leftward eye movements

Neglect of near versus far space - Halligan & Marshall (1991) ● Single case study (patient ‘TM’) - Line bisection task - Near (peripersonal) space (0.tim) → ‘TM’ showed severe left neglect ● Far (extrapersonal) space (at 2.tim) - light pointer, darts - No neglect (accurate bisection) ● Opposite pattern observed in five other patients ● All showed neglect for far space not near space – Cowey, Small, & Ellis. (1994) Perceptual versus motor neglect ● Line bisection using a pulley system [1] Congruent condition: move pointer (triangle) directly [2] Non-Congruent condition: move string section (square) which moves pointer in opposite direction ● Some patients showed deficits in making leftward movement in incongruent condition – motor neglect (moving square to right moves pointer into left neglected side of space) - Bisiach, et al. (1990)

Cancellation task – Normal view or mirror viewing – Tegner & Levander, (1991) ● Perceptual neglect (ignore left side of reflection, which is right side of paper) ● Motor neglect (ignore left side of paper, which is right side of reflection)

Models of neglect (Bradshaw and Mattingley, 1995) ● Representational ● Attentional ● Premotor model Representational model of neglect - Bisiach and Luzzatti (1978) ● Neglect reflects a failure to construct a neural representation of the external environment ● Damage to one hemisphere assumed to impair the representation of the opposite

side of space Attentional model of neglect – Neglect reflects a failure to orient covert attention Posner’s attentional model of neglect (Posner et al. 1984) ● Shifts of attention require: Disengagement - move - re-engagement ● Patients showed increases in reaction time in responding covertly to a stimulus on the left, but only if a cue had previously appeared to the right side

● Shims of attention require: Disengagement - move - re-engagement ● Right hemisphere parietal damage produces a deficit of disengagement of attention from the right (ipsilesional) side of space ● Cannot disengage attention from right visual field but can disengage from left visual field Heilman’s Attention – Intention model (Heilman and Valenstein, 1979) ● ‘Attend’ and ‘Intend’ ● Attend – detect a stimulus Intend – initiate an appropriate response ● Right Hemisphere (R.H.) is dominant in spatial behaviour – Attention (attend and

intend) in both directions, L.H. only to right

● Neglect reflects a failure to attend and/or intend to contralesional (left) side of space ● The deficit of attention and intention in neglect is due to hypoarousal of damaged (right) hemisphere ● Space-related behaviour is subserved by a network of interconnected brain regions

Kinsbourne's Attentional model (Kinsbourne, 1970) ● Each hemisphere controls attentional orienting in contraversive direction – left hemisphere = rightward orienting – Right hemisphere = leftward orienting ● The left hemisphere has a stronger orienting bias ● In the intact brain these are balanced ● Following right brain damage the rightward vector is released from inhibition ‘Directional bias’ ● Right brain damage leaves intact left hemisphere overactive ● left hemisphere over-activity results in rightward orienting bias ● Neglect patients have deficit orienting attention to left and also show an ipsilesional (rightward) bias Testing a prediction from Kinsbourne's model - Ladavas et al. (1990) ● If neglect patients have rightward orienting bias, they should be better at shiming their attention to objects located further to the right ● Reaction times: - Neglect patients - fastest responses for targets in right box (far) - Patients without neglect faster for left box (near)

Using TMS on intact (left) overactive hemisphere to reduce neglect ● Brighina et al. (2003) - Repetitive TMS over intact (left) PPC ● 1Hz daily, 2 weeks ● 3 patients, left neglect reduced up to 15 days later ● Shindo et al. (2006) - 2 patients, left neglect reduced 6 weeks later Premotor Model of Neglect - Rizzolatti and Berti (1990, 1993) ‘Attention’ and ‘Action’ ● Can be viewed as a combination of attentional and representational accounts ● Attention involved in selection of an object for action ● Spatial attention involves multiple circuits which sub- serve different regions of space Three separate regions of space ● Personal - own body space ● Peripersonal – area around upper body within reaching distance ● Extrapersonal – beyond reaching distance ● Neural circuits - Personal and peripersonal - premotor cortex (Area 6) and inferior parietal cortex area PG - Extrapersonal – frontal eye fields and parietal area PF Premotor theory of Neglect - Rizzolatti and Berti (1993) ● Neglect is primarily a disorder of spatial awareness ● Spatial awareness arises from joint activity of several cortical and subcortical areas ● Combined neural activity in this neural circuit form representations for the control of goal-directed action ● Damage produces loss of awareness and the attentional deficits are a secondary consequence of damage to the spatial representations Motor responses - Goodale et al. (1990) ● Reach trajectories – amer right hemisphere damage ● Reaches skewed to right then corrected ● Shows the interrelatedness of attention and action

Summary ● Neglect is not a unitary syndrome - can affect near space and/or far space - can be object-based and/or space-based - can influence perceptual processing and/or motor responses ● Models - Attentional, Representational, Pre-motor ● Multiple forms of neglect may reflect damage to different brain circuits involved in the representation of space and in orienting of attention...