Medicine – Features of Parietal Lobe Lesions

The parietal lobe integrates sensory information and contributes to spatial awareness, body awareness, skilled purposeful movements, calculation, reading, writing, and visual–spatial processing.

The clinical features depend strongly on whether the lesion involves the dominant hemisphere, usually the left, or the non-dominant hemisphere, usually the right.

1. Dominant Parietal Lobe Lesions

The dominant parietal lobe is particularly important for:

Language-related functions.

Calculation.

Writing.

Reading.

Learned purposeful movements.

Lesions can therefore produce apraxia and several higher cortical deficits.

2. Apraxia

Apraxia is the inability to carry out a learned purposeful movement despite having adequate:

Strength.

Sensation.

Coordination.

Understanding of the command.

The patient knows what they want to do but cannot correctly organise the motor sequence.

3. Ideomotor Apraxia

Ideomotor apraxia means difficulty performing or imitating a learned gesture on command.

For example, the patient may be unable to:

Wave goodbye.

Pretend to use a key.

Salute.

Imitate the examiner’s hand gesture.

This is commonly associated with dominant parietal or connected frontal-parietal network lesions.

4. Acalculia

Acalculia is the acquired inability to perform calculations.

A patient may have difficulty with:

Addition.

Subtraction.

Multiplication.

Simple numerical manipulation.

It is classically associated with a lesion involving the dominant inferior parietal region.

5. Agraphia

Agraphia is an acquired inability or major impairment in writing.

The patient may have difficulty:

Writing spontaneously.

Writing to dictation.

Forming meaningful written words or sentences.

Dominant parietal lesions are an important cause.

6. Alexia

Alexia means acquired impairment of reading.

However, alexia is not produced only by parietal lesions. Its exact pattern depends on the affected language and visual pathways.

Dominant temporoparietal or occipitotemporal lesions may impair reading.

7. Gerstmann Syndrome

A classic dominant parietal syndrome is:

Gerstmann syndrome.

It is associated particularly with lesions of the:

Dominant angular gyrus.

The classic features are:

Acalculia.

Agraphia.

Finger agnosia.

Left-right disorientation.

This is a very useful localisation pattern.

8. Finger Agnosia

Finger agnosia is difficulty recognising, identifying, or naming individual fingers.

It is one of the classic components of:

Gerstmann syndrome.

9. Left-Right Disorientation

Patients may have difficulty distinguishing:

Left from right.

For example, they may be unable to follow a command such as:

“Touch your left ear with your right hand.”

This again suggests dominant parietal dysfunction.

10. Drawing Difficulty

The original note lists:

Drawing apraxia.

A broader and more useful term is:

Constructional apraxia.

The patient has difficulty organising spatial components into a meaningful whole.

They may struggle to:

Copy a cube.

Draw a clock.

Copy geometric shapes.

11. Non-Dominant Parietal Lobe Lesions

The non-dominant parietal lobe, usually the right hemisphere, is especially important for:

Spatial attention.

Awareness of the contralateral side of the body and environment.

Visual-spatial organisation.

Lesions can therefore cause striking neglect syndromes.

12. Hemispatial Neglect

A classic right parietal lesion causes:

Left hemispatial neglect.

The patient fails to attend to the left side of:

Their body.

Their surroundings.

This is not caused by blindness alone.

It represents failure of spatial attention.

13. Examples of Neglect

A patient with left-sided neglect may:

Eat food only from the right half of the plate.

Shave only the right side of the face.

Ignore people standing on the left.

Draw only the right half of a clock.

These are classic bedside clues.

14. Extinction

Sensory extinction is a milder attentional abnormality.

When each side is stimulated separately, the patient detects both.

However, when both sides are stimulated simultaneously, the patient ignores the stimulus on the side contralateral to the lesion.

For example:

Right parietal lesion → left-sided extinction.

15. Visual Extinction

The same phenomenon can occur with vision.

The patient may detect:

A left visual stimulus alone

and

A right visual stimulus alone,

but when both are presented simultaneously, only the right stimulus is reported.

16. Dressing Apraxia

Dressing apraxia is difficulty correctly orienting clothes relative to the body.

The patient may:

Put clothing on backwards.

Put an arm through the wrong opening.

Become unable to organise the sequence of dressing.

It is classically associated with:

Non-dominant parietal lesions.

17. Constructional Apraxia

Constructional apraxia may be particularly prominent in:

Non-dominant parietal lesions.

The patient has difficulty:

Drawing.

Copying designs.

Constructing geometric figures.

Arranging blocks into a pattern.

Although it can occur with lesions in either hemisphere, right parietal dysfunction is especially associated with severe visuospatial constructional impairment.

18. Anosognosia

A non-dominant parietal lesion may cause:

Anosognosia.

This means lack of awareness or denial of a neurological deficit.

For example, a patient with severe left-sided weakness may insist:

“There is nothing wrong with my arm.”

This is especially associated with right hemisphere lesions.

19. Body-Schema Disturbance

The parietal lobe helps construct an internal representation of the body.

Lesions may therefore cause abnormal awareness of:

Body position.

Body parts.

The relationship between the body and surrounding space.

This contributes to neglect, dressing problems, and other higher-order deficits.

20. Astereognosis

Astereognosis is inability to recognise an object by touch despite intact primary sensation.

For example, with the eyes closed, the patient may be unable to identify a:

Key.

Coin.

Pen.

even though they can feel its shape and texture.

21. Cortical Sensory Function

Recognition of an object by touch requires intact:

Primary sensation

plus

Parietal cortical interpretation.

Therefore:

Normal primary sensation + inability to identify object by touch = astereognosis.

22. Graphesthesia

Another cortical sensory function is:

Graphesthesia.

This is the ability to recognise a number or letter traced on the skin.

A parietal lesion may impair this ability despite preserved basic touch sensation.

23. Two-Point Discrimination

Parietal cortical dysfunction may also impair:

Two-point discrimination.

The patient becomes less able to distinguish two simultaneous nearby points of contact.

This is another form of cortical sensory impairment.

24. Sensory Inattention

The patient may ignore sensory information from the side opposite the lesion.

This may appear as:

Tactile extinction.

Visual extinction.

Auditory extinction.

It is especially characteristic of non-dominant parietal lesions.

25. Inferior Homonymous Quadrantanopia

The parietal lobe contains the:

Superior optic radiations.

These fibres carry information from the:

Contralateral inferior visual field.

Therefore, a parietal lesion can cause:

Contralateral homonymous inferior quadrantanopia.

26. “Pie on the Floor”

The classic mnemonic is:

Parietal = pie on the floor.

This means:

Parietal optic radiation lesion → contralateral inferior quadrantanopia.

27. Why the Field Defect Is Inferior

The superior optic radiation carries information representing the:

Inferior visual field.

Therefore:

Superior parietal optic radiation damaged → inferior visual field lost.

28. Example of a Parietal Visual Field Lesion

A lesion in the:

Left parietal lobe

may cause:

Right homonymous inferior quadrantanopia.

A right parietal lesion may cause:

Left homonymous inferior quadrantanopia.

29. Parietal versus Temporal Visual Field Defects

Parietal lesion:

Contralateral inferior quadrantanopia.

“Pie on the floor.”

Temporal lesion:

Contralateral superior quadrantanopia.

“Pie in the sky.”

30. Sensory Loss

Parietal lesions may also produce:

Contralateral sensory impairment, particularly if the primary somatosensory cortex is affected.

Possible abnormalities include reduced:

Touch.

Proprioception.

Cortical sensory discrimination.

31. Primary Somatosensory Cortex

The primary somatosensory cortex is located in the:

Postcentral gyrus.

Damage can cause:

Contralateral sensory loss.

The exact distribution depends on which part of the sensory homunculus is affected.

32. Dominant Parietal Lobe – Note Form

Apraxia:

Difficulty performing learned purposeful movements despite intact strength and comprehension.

Acalculia:

Unable to calculate.

Agraphia:

Unable to write normally.

Alexia:

Reading impairment may occur depending on lesion extent.

Gerstmann syndrome:

Acalculia.

Agraphia.

Finger agnosia.

Left-right disorientation.

33. Non-Dominant Parietal Lobe – Note Form

Hemispatial neglect:

Usually left neglect from right parietal lesion.

Extinction:

Contralateral stimulus ignored during bilateral simultaneous stimulation.

Dressing apraxia:

Difficulty orienting clothing to the body.

Constructional apraxia:

Difficulty copying, drawing, or constructing spatial patterns.

Anosognosia:

Lack of awareness of neurological deficit.

34. Features Possible with Either Side

Astereognosis:

Unable to recognise an object by touch despite intact basic sensation.

Agraphesthesia:

Unable to recognise numbers or letters traced on the skin.

Constructional difficulties:

Can occur with either hemisphere but are often more striking with non-dominant parietal lesions.

Contralateral inferior quadrantanopia:

Due to involvement of superior optic radiations.

35. Dominant versus Non-Dominant Hemisphere

The dominant hemisphere is usually:

Left

in most right-handed people and many left-handed people.

It is particularly important for:

Language.

Writing.

Calculation.

Praxis.

The non-dominant hemisphere is usually:

Right.

It is particularly important for:

Visuospatial attention.

Spatial awareness.

Body awareness.

Constructional ability.

36. Causes of Parietal Lobe Lesions

Possible causes include:

Stroke.

Brain tumour.

Traumatic brain injury.

Demyelination.

Cerebral infection or inflammation.

Neurodegenerative disease.

Stroke is an especially important cause of sudden parietal deficits.

37. Parietal Stroke

A dominant parietal stroke may produce:

Acalculia.

Agraphia.

Apraxia.

Language-related deficits.

A non-dominant parietal stroke may produce:

Severe contralateral neglect.

Dressing apraxia.

Constructional impairment.

38. Important Corrections to the Original Notes

Ideomotor apraxia is not exclusively a non-dominant parietal sign. It is more classically associated with dominant hemisphere frontoparietal networks, although apraxic disturbances can occur with lesions affecting wider networks.

Constructional apraxia can occur with lesions of either hemisphere but is particularly associated with non-dominant/right parietal dysfunction.

Astereognosis requires preserved basic sensation. If the patient cannot feel the object properly because of primary sensory loss, the finding cannot be called true astereognosis.

Alexia is not uniquely a parietal sign. Reading depends on distributed visual-language networks, including occipital, temporal, and parietal regions.

The original description of the visual pathway as the “upper loop of optic radiation” is better expressed as:

Superior optic radiations passing through the parietal lobe.

Damage produces:

Contralateral homonymous inferior quadrantanopia.

Key Clinical Pattern

Think of the dominant parietal lobe as:

CALCULATION + WRITING + PRAXIS.

Remember:

GERSTMANN = ACALCULIA + AGRAPHIA + FINGER AGNOSIA + LEFT-RIGHT DISORIENTATION.

Think of the non-dominant parietal lobe as:

SPACE + ATTENTION + BODY AWARENESS.

Therefore:

RIGHT PARIETAL LESION → LEFT-SIDED NEGLECT ± DRESSING APRAXIA ± ANOSOGNOSIA.

For cortical sensation:

ASTEREOGNOSIS = CAN FEEL IT BUT CANNOT IDENTIFY IT BY TOUCH.

For vision:

PARIETAL → CONTRALATERAL INFERIOR QUADRANTANOPIA = “PIE ON THE FLOOR.”