B2 L1 - Disorders of the parietal lobe

parietal lobe location

between the frontal lobe and occipital lobe, above temporal lobe; influences which part of the brain is used next

information processing pathways of the brain

dorsal and ventral; info comes into visual cortex from eyes then goes to one or the other

dorsal pathway

where things are in space, involves parietal cortex (how we act on the info)

ventral pathway

what things are in space

attentional control network

top-down decisions competing with bottom-up processing stream

top-down decisions in the attentional control network

parietal lobe passes info to the frontal cortex, where we then make a decision on what we’re going to act on in the environment

bottom-up processing stream in the attentional control network

in constant communication with top-down decision making, passes info up to the frontal cortex and tries to drag attention towards a sensory input

functions of the parietal cortex

space-based, feature-based, object-based attention; reaching and grasping; magnitude processing

neuropsychological disorders of the parietal lobe

depend on location and hemisphere of the lesion, following events like a stroke you rarely see specific impairments and generally people can recover after a period of time

key symptoms of hemispatial neglect

damage to right parietal lobe, don’t attend to the left side of space (impacts perception and

assessing neglect

eye tracking, Piazza del Duomo

order of processing from visual info

info comes in from left visual field, first processed in right visual cortex then proccessed in the parietal lobes

right hemisphere has dominacne for visuo-spatial cortex

processes info from both contralaterl and ipsilateral eye fields, left parietal cortex can only represent info from contralateral visual field

damage to left hemisphere is unlikely to cuase deficit because

right hemisphere can compensate and sees both visual fields

right hemisphere damage means

only left hemisphere works, and can only process the right visual field of space → neglect

neglect in the auditory domain

sounds coming from left side perceived as coming from the right, or the ipsilesional side of space; deficits are specific to contralesional side of space

recovery of neglect

can be spontaneous, occur with time; once patients are aware of their impairment they can begin to work on strategies such as how they orient towards objects

Kim et al, applied rTMS over unaffected parietal lobe

sig improvements on line bisection and line cancellation tests found in rTMS application 10x over only once

Bálint’s syndrome

disorder of object-based attention, bilateral lesions of parietal and occipital lobe

key symptoms of Bálint’s syndrome

simultanagnosia, optic apraxia, oculomotor apraxia

simultanagnosia

if you present someone with multiple objects, the patient will only be able to attend to one of the objects at a time - unlike neglect because objects can be anywhere in visual field and symptom will persist (combining objects helps perception and occlusions make it more difficult)

optic ataxia - patient with bilateral damage affecting dorsal system

parietal lobe lesions (where pathway), could see shape of objects and tell them apart, but grasped at inappropriate points

optic ataxia - bilateral damge affecting ventral visual stream

ventral occipital lobe lesions (what pathway), performed at chance when seeing and recognizing objects but able to grasp them successfully

orientation and position errors in ataxia patients

unable to place their hands through a slot, and either had their hand at the wrong angles or tried to insert at the wrong places

optic ataxia can be caused by lesions occurring in the

right, left or both inferior parietal lobes

oculomotor apraxia

problem making planned and purposeful eye movements, needs to move the whole head to make eye contact

cause of oculomotor apraxia

damage to parietal lobe causes disconnect to frontal eye fields, particularly damage to the dorsal pathway

treatment of Bálint’s syndrome

very little evidence for effective strategies to improve impairments but eye movement training, convergence exercies and word reading practice has improved symptoms in single case studies

dyscalculia

disorder of magnitude processing, is a neurodevelopmental disorder (distinct from acalculia which is caused by acquired damage), locatedin right inferior parietal lobe

patients either dyscalculia tend to have a problem

understanding and manipulating numbers (arithmetic, multiplication, etc.)

numerical distance effect

easier to identify the larger of two numbers when there is a greater numerical distance between them

Price et al, numerical distance effect

controls showed greater activations within right intraparietal sulcus when working with close or far number distances, children with dyscalculia didn’t show this effect

other symptoms of dyscalculia

diffculty reading analogue clocks, with multiplication, conceptualizing time, differentiating left and right, visualizing mentally, choreographed dancing

a theory of magnitude (ATOM)

time, space and number share a common neural underpinning in the right intraparietal sulcus

effect of low frequency rTMS

suppresses excitability of cerebral cortex

effect of high frequency rTMS

inc excitability of cerebral cortex

effect of applying low frequency magnetic stimulation over unaffected lobe

more effective than high-frequency stimulation of affected lobe, has a knock-on effect to increase activity of affected lobe

ego-centric neglect

neglect stimulation from the left side when the head/body is centered (viewer centered), related to dorsal visual pathway

allocentric neglect

completely neglect left half of objects whether they are placed on left side or right side (object- centered), related to ventral visual pathway

better improvements to allocentric than egocentric neglect after 10 sessions of rTMS because

allocentric neglect patients have wider brain lesions, leading to severe symptoms