Agnosia, Apraxia & Neglect

The higher cortical syndromes are some of the most fascinating findings in clinical neurology. A patient can see normally but not recognize a face; can move normally but not pantomime brushing their teeth; can have full motor and sensory function on the left side but behave as if it does not exist. Each of these patterns reflects a specific failure in the way the cortex transforms perception into meaning, intention into action, or attention into awareness. None of them is rare. All of them are routinely missed unless the examiner specifically looks for them.

This page covers three families of higher cortical syndromes: agnosia (failure to recognize despite intact perception), apraxia (failure to perform learned movement despite intact motor function), and neglect (failure to attend to one side of space despite intact sensory function). Each is defined by a dissociation: the basic input or output is preserved, but the higher cognitive integration of it is not. Recognizing these syndromes at the bedside requires knowing what to ask for; none of them surfaces on a routine “neuro-intact” exam.

Where the higher cortical syndromes localise — a hemispheric division of labour:

The one rule to remember: neglect and anosognosia are right-hemisphere; apraxia and Gerstmann are left-hemisphere; the visual agnosias and Bálint are bilateral.

Agnosia — Failure of Recognition

Agnosia is the inability to recognize objects, faces, sounds, or other sensory information despite intact primary sensation. The patient sees the watch on the table but cannot identify it as a watch. The patient hears the bell ringing but cannot say what the sound is. The patient feels the key in their hand but cannot name it without looking. Each modality has its agnosias, and each agnosia is defined by what fails and what is preserved.

The unifying principle: agnosia is a disconnection between perception and meaning. The sensory cortex is intact (the patient can describe the visual features of the watch — round, metal, with marks around the edge), but the link to stored conceptual knowledge is broken (they cannot say what the object is for or how it is used). Different agnosias arise from lesions at different points in this pathway.

Visual Agnosia

The classical distinction is between two types of visual agnosia:

• Apperceptive visual agnosia: failure of basic visual integration. The patient cannot recognize a watch because the elementary visual features have not been assembled into a coherent percept. They cannot copy a simple drawing because they cannot perceive the shape to begin with. The lesion is in the bilateral occipital cortex, often after diffuse hypoxic injury or carbon monoxide poisoning.
• Associative visual agnosia: failure of the link between intact perception and meaning. The patient sees the watch clearly, can copy a drawing of it accurately, can describe its features in detail — but cannot say what it is. Show them the watch and they say “a round metal disc with markings”; place it in their hand and they immediately identify it (“oh, a watch!”). This dissociation between vision and touch is diagnostic. The lesion is typically in the bilateral inferior occipitotemporal cortex.

The bedside test of associative visual agnosia is to show the patient an object and ask “what is this?” and “what is it used for?” without letting them touch it. If they fail visually but succeed by touch, the diagnosis is made. Drawings or photographs can be substituted for real objects.

Prosopagnosia (Face Agnosia)

Prosopagnosia is the inability to recognize faces. Patients describe an inability to identify family members, friends, and even themselves in a mirror, while general visual function is intact. They can describe a face in detail — the color of the eyes, the shape of the nose, whether the person is smiling — but cannot link the face to a known identity. They typically recognize people instead by voice, gait, hairstyle, or clothing.

The lesion is in the bilateral fusiform face area, in the medial occipitotemporal cortex (the fusiform gyrus). Unilateral right-sided lesions can produce partial deficits, but the most severe prosopagnosia requires bilateral involvement. The most common cause is bilateral posterior cerebral artery infarction; degenerative disease (semantic dementia, posterior cortical atrophy) can also produce it. Developmental prosopagnosia — congenital, sometimes familial — is increasingly recognized.

Color Agnosia and Achromatopsia

Two related but distinct deficits affect color processing. Cerebral achromatopsia is loss of the perception of color itself — the world appears in grayscale. The lesion is in the fusiform gyrus (V4 region), often unilateral. The patient with hemiachromatopsia sees color in one hemifield and gray in the other.

Color agnosia is preserved color perception but failure to associate colors with their names or to know what color objects “should be.” The patient correctly distinguishes red from green but cannot tell you the color of an apple or a banana from memory. The lesion is typically left-sided posterior cortical, often accompanying pure alexia (which is essentially a “word agnosia”).

Auditory Agnosia

Failure to recognize sounds despite intact hearing. Several subtypes:

• Pure word deafness: inability to recognize spoken words while non-verbal sounds and reading are preserved. The patient hears the words but cannot understand them. Lesions are bilateral or dominant superior temporal cortex, sparing Wernicke area.
• Non-verbal auditory agnosia (environmental sound agnosia): the patient cannot identify a ringing telephone, a barking dog, or running water as familiar sounds, but understands speech normally.
• Amusia: loss of the ability to recognize, produce, or appreciate music. Acquired amusia is uncommon and most often seen with right-hemisphere lesions.

Tactile Agnosia (Astereognosis)

Failure to recognize objects by touch despite intact primary sensation. The patient feels the key in their hand, can describe its shape, weight, and temperature, but cannot identify it as a key without seeing it. The lesion is in the parietal cortex contralateral to the affected hand. Astereognosis is one of the cortical sensory findings discussed in detail on the cortical sensation page; in the agnosia framework, it represents the tactile equivalent of associative visual agnosia.

Anosognosia and Specific Body Agnosias

Anosognosia is unawareness of a neurological deficit — the patient denies their hemiplegia, hemianopia, blindness, or aphasia. It is most striking with right parietal lesions, where a dense left hemiparesis is denied or rationalized (“my arm is just tired”). Hemiplegia is the classical context, but anosognosia for cortical blindness (Anton syndrome) is even more dramatic: the patient with bilateral occipital infarction confabulates visual experience while bumping into the furniture they claim they can see.

Asomatognosia is loss of awareness of part of one’s body. The patient may fail to recognize their own paralyzed limb, sometimes claiming it belongs to someone else (somatoparaphrenia). Severe forms can include claims that the limb has been stolen or replaced.

Autotopagnosia is the failure to identify or localize parts of one’s own body on request — the patient cannot point to their elbow when asked, despite being otherwise able to follow commands. The lesion is typically left parietal.

Finger agnosia is a specific autotopagnosia for the fingers — the patient cannot name or identify their own fingers. It is one of the four components of Gerstmann syndrome (see below).

Apraxia — Failure of Learned Movement

Apraxia is the inability to perform learned, skilled movements despite intact motor power, sensation, coordination, and comprehension. The patient who is asked to pretend to brush their teeth fumbles ineffectively, perhaps making a vague flapping movement near their face, although the same patient can shake your hand, walk, and lift objects normally. Apraxia is a disorder of the conceptual-motor interface: the patient knows what they want to do but cannot translate that intention into the correct motor program.

The diagnosis requires that all the elements needed for the movement be intact:

• The patient must understand the command (rules out aphasia and dementia as primary explanations).
• The patient must have intact motor power on the side being tested.
• The patient must have intact sensation and coordination.

If all of these are present and the movement still fails — particularly to pantomime or imitation — the diagnosis is apraxia.

Testing for Apraxia

The bedside exam tests apraxia in three modes of increasing difficulty:

1. To verbal command: “Show me how you would brush your teeth.” “Pretend to comb your hair.” “Wave goodbye.”
2. To imitation: demonstrate the movement and ask the patient to copy it.
3. With the actual object: give the patient the toothbrush and ask them to use it.

Patients with mild apraxia may fail to pantomime but succeed with imitation or the real object. Patients with severe apraxia fail in all three modes. The hierarchy of preserved performance is a useful indicator of severity.

Watch for specific error types:

• Spatial errors: the movement is in the wrong plane (combing the hair by moving the hand horizontally instead of vertically).
• Temporal errors: the rhythm or sequence is wrong.
• Body-part-as-object errors: the patient uses their finger as the toothbrush (sliding the finger across the teeth rather than holding an imaginary toothbrush). This is a particularly characteristic apraxic error.
• Perseveration: the patient repeats a previous movement instead of producing the requested one.

Classification of Apraxia

The traditional classification distinguishes several types, which differ in the deficit, how you elicit it, and where they localise:

The Apraxia of Corticobasal Syndrome

Corticobasal syndrome is a degenerative disorder defined in large part by a particular kind of apraxia: an asymmetric limb apraxia with prominent ideomotor and limb-kinetic features, often accompanied by alien limb phenomenon, dystonia, and rigidity. The affected hand may move “of its own accord,” may not respond to commands, may interfere with the other hand’s attempts to act. The pathology is most often a tauopathy, but the corticobasal clinical syndrome can be produced by several different underlying pathologies.

Neglect — Failure of Attention

Neglect is the failure to attend to, respond to, or orient toward stimuli on the side opposite a brain lesion despite intact primary sensation and motor function. The patient with severe left neglect may eat from only the right half of the plate, dress only the right side of the body, draw only the right half of a clock, fail to notice people standing on their left, and even fail to acknowledge their own paralyzed left arm. The deficit is one of attention and representation, not of perception itself.

Neglect is almost always a right-hemisphere syndrome producing left-sided neglect. The right hemisphere appears to manage attention to both sides of space, while the left hemisphere manages attention primarily to the right. Right-hemisphere lesions therefore deprive the left hemisphere’s attention to the right side of having a counterweight, while the right hemisphere’s special role is lost. Left-hemisphere lesions, by contrast, are compensated by the right hemisphere’s ongoing attention to both sides.

The Components of Neglect

Neglect has several modality-specific components that can be assessed separately:

• Sensory neglect (extinction): the patient detects a stimulus on either side in isolation but fails to detect the contralesional stimulus when both sides are stimulated simultaneously. Test by touching one hand, then the other, then both — extinction is failure of the affected side under double stimulation. This can be tested in tactile, visual, and auditory modalities.
• Visual neglect: failure to attend to objects in the contralesional visual hemifield even with intact visual fields. The clinical test is line bisection (the patient is asked to mark the midpoint of a horizontal line and marks it well to the right of center), cancellation tasks (asked to cross out all the symbols on a page, the patient omits the left side), and drawing tasks (the clock face has all the numbers crowded on the right).
• Motor neglect: failure to spontaneously use the contralesional limb despite intact motor function. The patient may have a normal motor exam on formal testing but never moves the left arm spontaneously.
• Personal neglect: failure to attend to the contralesional half of one’s own body. Patients may shave only the right side of the face, dress only the right side.
• Representational neglect: failure to attend to the contralesional half of mental images. Asked to describe a familiar landmark from a particular vantage point, the patient omits objects on what would be the left side; asked to describe it from the opposite vantage, they now mention the previously omitted objects but omit those that are now on their left.

The Bedside Examination of Neglect

Several quick tests reveal neglect that a routine exam misses:

• Confrontation visual fields with simultaneous bilateral stimulation: wiggle your fingers in both hemifields at once. The neglecting patient detects only the right (and may say “right” or fail to see the left at all).
• Tactile extinction: touch one hand, the other, then both. The patient reports only the right under double stimulation.
• Line bisection: ask the patient to mark the middle of a horizontal line on paper. The mark is to the right of center.
• Cancellation tasks: ask the patient to cross out all the As (or stars, or circles) on a page sprinkled with various symbols. The neglecting patient omits the left side.
• Clock drawing: the numbers are crowded on the right side, or the left side is missing entirely.
• Spontaneous behavior: watch the patient eating, dressing, or being interviewed. Neglect declares itself in the way the patient orients to the room and uses their body.

Neglect versus Hemianopia

Patients with hemianopia compensate by turning the head and eyes to scan the affected hemifield. Patients with neglect do not — they may have intact fields on formal testing but still ignore the affected side. The patient with both deficits is doubly impaired and at high functional risk.

The bedside distinction is that the hemianopic patient knows what they cannot see (they bump into things on the left and learn to compensate); the neglecting patient does not (they do not know there is anything to compensate for, and they deny the deficit).

Anosognosia for Hemiplegia

Anosognosia — denial of deficit — is one of the most striking accompaniments of neglect. The patient with a dense left hemiplegia from a right MCA stroke may insist that they are not weak. Asked to lift the paralyzed arm, they may produce no movement and then claim it has moved, may complain that the arm “doesn’t feel like mine,” or may rationalize the failure (“the arm is just tired”). The combination of dense hemiplegia, left neglect, and anosognosia is the classical picture of right MCA infarct.

Gerstmann Syndrome

The Gerstmann syndrome is a classical higher-cortical syndrome defined by the tetrad of:

1. Finger agnosia: inability to identify or name one’s own fingers.
2. Right-left disorientation: inability to distinguish right from left, in self or in others.
3. Acalculia: inability to perform basic arithmetic.
4. Agraphia: inability to write.

The lesion is in the dominant angular gyrus. Pure Gerstmann syndrome with all four components and no other deficits is uncommon; partial pictures are more typical. The combination can be seen with strokes, tumors, and degenerative disease in the dominant parietal lobe.

Balint Syndrome

A rare and striking syndrome from bilateral parieto-occipital damage, classically combining three deficits:

1. Simultanagnosia: inability to perceive more than one object at a time. The patient sees the spoon but not the rest of the table; once they shift attention to the cup, the spoon disappears from awareness. Asked to describe a picture, they describe one element at a time without integrating them.
2. Optic ataxia: inability to reach accurately under visual guidance. The patient reaches past or beside the target, although visual fields and motor function are intact.
3. Ocular apraxia: inability to voluntarily direct the eyes to a target. Smooth pursuit is preserved; saccadic gaze-shifting is not.

The most common cause is bilateral watershed infarction in the parieto-occipital territory, as seen after global hypoperfusion. Posterior cortical atrophy, a variant of Alzheimer disease, can also produce Balint syndrome over years.

Pitfalls and Pearls

• Agnosia requires intact primary perception. A patient with cortical blindness or a severe hemianopia cannot be said to have visual agnosia; the basic input has failed.
• The dissociation between modalities is the key. A visual agnosic identifies the object by touch; an associative visual agnosic copies the drawing perfectly but cannot name what they have drawn. Look for these dissociations.
• Apraxia presumes intact motor function and comprehension. The patient must be strong enough and attentive enough to follow the command; the failure is in the translation from intention to action.
• Body-part-as-object errors are highly characteristic of ideomotor apraxia. Watch for the finger used as a toothbrush.
• Neglect is almost always right-hemisphere. A patient with left neglect after a right MCA stroke is a recurring pattern; the reverse is rare.
• Always test for extinction. Double simultaneous stimulation reveals neglect that single-side testing misses. Tactile and visual extinction are quick to test and frequently positive.
• Anosognosia complicates rehabilitation. A patient who denies the deficit cannot motivate to overcome it. Recognition of anosognosia early in stroke care is essential for therapy planning.
• Constructional apraxia in a previously well-functioning patient is a useful early sign of Alzheimer disease and other parietal neurodegeneration. Ask the patient to draw a clock; the result is diagnostic of more than the patient or family realizes.
• Posterior cortical atrophy presents with the higher cortical syndromes — Balint, Gerstmann, alexia, apraxia — long before the memory complaints that the patient’s family expects from Alzheimer disease. A patient who got lost driving, who cannot read the small print, who can no longer dress themselves but has good memory, may have posterior cortical atrophy.
• The classical syndromes (Gerstmann, Balint, prosopagnosia) are still useful even though pure forms are uncommon. Recognizing the constellation tells you the localization and the family of pathologies even when the picture is incomplete.

References

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