Perception › Body Image Disturbance

Hemiasomatognosia

Hemiasomatognosia is a loss of the felt sense that one side of the body, most often the left, belongs to or is part of the self, typically following damage to the opposite side of the brain. The affected side may feel absent, foreign, or simply fail to register in the person's spontaneous awareness of their own body.

This has traditionally been treated as one of the clearest demonstrations that the sense of bodily ownership depends on active, ongoing brain processing rather than being an automatic given, since a structurally intact limb can drop entirely out of felt awareness after a focal lesion.

Recognition features

• A loss of the felt sense that one side of the body belongs to the self, most commonly the left side
• Usually follows a focal lesion in the hemisphere opposite the affected side, especially the parietal lobe
• The affected limb or side may simply fail to be mentioned or attended to, rather than being actively described as foreign
• Often occurs together with other neurological signs such as weakness or sensory loss on the same side

Eliciting it at interview

• Watch spontaneous behaviour as much as verbal report, since the affected side may simply be neglected in movement, dressing, or grooming without the person commenting on it
• Ask directly and specifically about each side of the body in turn: "Does this arm feel like it's part of you the same way this one does?"
• Distinguish carefully from simple weakness by testing whether the person spontaneously incorporates the limb into their account of their own body at all

Distinguishing features

• Differs from somatoparaphrenia, in which the person does not merely fail to register the limb but actively and elaborately denies it is theirs, sometimes attributing it to someone else
• Differs from hemispatial neglect, which is a failure to attend to one side of external space generally, not specifically the felt ownership of one's own body
• Differs from anosognosia, which is unawareness of a deficit such as paralysis rather than unawareness of the limb itself

Common misconceptions

• That hemiasomatognosia and somatoparaphrenia are simply two names for the same thing; they sit on a spectrum but the active, elaborated denial of ownership in somatoparaphrenia is a further and more striking step
• That the affected limb is truly numb or paralysed in every case; the disturbance is of felt ownership and attention, which can occur alongside, but is not identical to, sensory or motor loss

Related phenomena

Body Image Disturbance

Practice this

Following a right parietal lesion, a man simply fails to mention or attend to his left arm at all — when asked directly, he does not actively claim it belongs to someone else, he just seems to have lost the felt sense that it is part of him and rarely refers to it. What is this? · A patient with left-sided weakness, when asked directly about her left arm, insists with conviction that it belongs to her sister and offers a detailed explanation of how it supposedly came to be attached to her body. Before revealing the answer: is this hemiasomatognosia? · A patient with a right hemisphere lesion shows an odd relationship to their left limb. Before revealing the answer, decide what distinguishes hemiasomatognosia from somatoparaphrenia. · A patient fails to attend to one side following a right parietal lesion. Before revealing the answer, decide what distinguishes hemispatial neglect from hemiasomatognosia. · You are examining a patient with a right parietal lesion and want to assess for hemiasomatognosia. Before revealing the answer, decide what you would look for. · Explain why hemiasomatognosia is considered a milder or earlier disturbance than somatoparaphrenia, rather than simply a different, unrelated finding.

Illustration

A 71-year-old man recovering on a stroke ward consistently keeps his left arm tucked out of sight beneath the blanket and never once refers to it while describing how he is feeling, even when a nurse gently lifts it into view; when asked directly whether it feels like part of him, he pauses and says only that he 'hadn't really thought about it.'

References

• Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 3, 'Disorders of Perception'.