Basic Neurosciences · Paper A
Parietal lobe functions
The parietal lobeThe part of the brain near the crown of the head, involved in touch sensation and spatial awareness.Read more → sits at the top-and-back of the brain and blends together touch, vision and a sense of space, letting you sense where your body and nearby objects are. Damage here produces distinctive problems that differ by side, e.g. a patient who eats only the food on the right half of their plate and shaves only the right half of their face, unaware anything is missing. That pattern points straight to a non-dominant parietal lesion. In practice, the side of the lesion, not just its presence, decides which specific deficit to expect.
Damage to the non-dominant (usually right) parietal lobeThe part of the brain near the crown of the head, involved in touch sensation and spatial awareness.Read more → causes neglect of the opposite side of space, anosognosiaA lack of awareness or insight that one is unwell, caused by the illness itself.Read more → (being unaware of one's own deficit, such as not recognising a paralysed limb) and trouble dressing or copying drawings. A right parietal stroke can leave a patient insisting their left arm 'belongs to someone else': that is anosognosia, not confusion or denial. Damage to the dominant (usually left) angular gyrus causes Gerstmann syndrome: an inability to write, to calculate, to name fingers, and to tell left from right. A touch-based sign such as astereognosis (being unable to identify an object by feel despite normal basic sensation) should be tested separately from vision and calculation. The angular gyrus also contributes to object naming, so a lesion there can produce anomia (word-finding difficulty for objects) alongside the other Gerstmann features. On the non-dominant side, the right supramarginal gyrus is important for empathy, helping a person override their own immediate emotional perspective (emotional egocentricity) to correctly judge how someone else feels.
A vignette gives a side-specific parietal sign and asks you to localise it. Contralateral neglect and dressing difficulty point to the non-dominant lobe; Gerstmann's tetrad of agraphia, acalculia, finger agnosiaThe inability to recognise familiar objects, sounds, or faces despite normal senses.Read more → (agnosia meaning an inability to recognise something despite intact senses) and left-right disorientation points to the dominant lobe.
The sits at the top and back of the brain, and its whole job is to blend touch, vision and body-position sense into one map of space. When it is damaged, the deficit it produces depends heavily on WHICH side is hit, not just that the lobe is hit. That side-dependence is the single idea every exam question on this topic is built around, so hold it in mind through every section below.
The is one of the four main lobes of the cerebral cortex (the folded outer layer of the brain), sitting behind the and above the temporal and . It receives touch and position information from the body (via the postcentral gyrus, a strip of cortex just behind the central sulcus) and combines this with visual input from the occipital lobe to build an internal sense of where the body is and where objects are around it. In most people, the left parietal lobe is the dominant side for language-linked skills like calculation and writing, while the right, non-dominant, side is dominant for spatial attention.
Most candidates assume any parietal lesion causes the same vague 'confusion' or 'clumsiness'. It does not. A dominant, usually left, lesion at the angular gyrus (a specific patch of parietal cortex near the junction with the temporal and ) produces a different, nameable syndrome from a non-dominant, usually right, lesion. Learn the SIDE first, then the sign: guessing the sign without fixing the side is the commonest exam trap.
Imagine your brain needs two separate jobs done: knowing WHERE something is in space, and knowing WHAT symbolic operations to do with numbers and letters (like adding two numbers or writing a word). The non-dominant specialises in the first job, spatial attention across the whole environment. The dominant parietal lobe specialises in the second, symbolic manipulation such as calculation and writing. Damage to the first job produces neglect (ignoring one side of space); damage to the second produces Gerstmann syndrome, a cluster of symbolic deficits. Keeping these two jobs mentally separate predicts which signs go together.
Non-dominant (usually right) parietal lesion: causes hemispatial neglect (ignoring people, objects or even one's own limb on the opposite, usually left, side of space, despite intact vision), (unawareness of one's own deficit, e.g. denying a paralysed arm is even weak), dressing apraxia (difficulty organising clothes onto the body) and constructional apraxia (difficulty copying a simple drawing such as a clock face).
Dominant (usually left) angular gyrus lesion, Gerstmann syndrome: a specific tetrad of acalculia (inability to perform calculation), agraphia (inability to write), finger (inability to name or identify individual fingers) and left-right disorientation. All four together, in a patient with a left parietal lesion, is the classic exam picture.
Supramarginal gyrus lesion: ideomotor apraxia, difficulty performing a learned motor task on command (such as miming brushing teeth) despite normal strength and comprehension of what is being asked.
Astereognosis: an inability to identify an object purely by feel, with eyes closed, despite normal basic touch sensation being present. This is a specific parietal integration deficit, not a peripheral sensory nerve problem.
Bilateral parieto-occipital damage, Balint syndrome: a rare triad of simultanagnosia (being able to perceive only one object at a time, unable to take in a whole visual scene), optic (mis-reaching for an object seen in the periphery despite normal limb strength) and oculomotor apraxia (difficulty voluntarily shifting gaze on command).
Neglect is a disorder of ATTENTION across all senses, not a visual field defect: a patient with neglect may have a fully intact visual field on formal testing yet still bump into furniture on their neglected side, e.g. a patient who repeatedly collides with objects on the left despite a normal visual field. This is the single most tested distinction on this topic. Gerstmann syndrome (dominant parietal) is distinguished from non-dominant neglect by WHICH side is damaged and by the presence of calculation and writing deficits rather than spatial inattention. Astereognosis (parietal, touch-based) is distinguished from visual (occipital, vision-based) by testing the affected sense in isolation.
Bedside testing includes asking the patient to copy a clock face or simple drawing (for constructional apraxia), asking them to identify fingers by name or perform calculations (for Gerstmann syndrome), and testing double simultaneous stimulation, touching both sides of the body at once to reveal subtle neglect that single-side testing misses. Structural brain imaging, usually MRI, localises the lesion (commonly stroke, tumour or trauma) and confirms which side and which specific parietal region is affected.
There is no drug that reverses a parietal lesion; management is rehabilitation-led. Occupational therapy and neuropsychology teach compensatory strategies for neglect, such as deliberately scanning to the affected side, and physiotherapy addresses associated motor deficits. Speech and language therapy supports patients with associated language or calculation deficits. Underlying causes, such as an acute stroke, are managed per standard stroke pathways (including NICE stroke guidance), since the parietal signs themselves are a marker of the lesion, not a separate disease to treat directly.
When a vignette describes a parietal sign, decide the SIDE first (dominant versus non-dominant), because that single decision narrows the syndrome to either Gerstmann's symbolic tetrad or non-dominant spatial neglect before you even read the specific symptom list.
The damage pattern is set by which side is hit: dominant gives Gerstmann's symbolic deficits, non-dominant gives spatial neglect and .