Body schema
The neurologist Sir Henry Head originally defined it as a postural model of the body that actively organizes and modifies 'the impressions produced by incoming sensory impulses in such a way that the final sensation of body position, or of locality, rises into consciousness charged with a relation to something that has happened before'.
[1] As a postural model that keeps track of limb position, it plays an important role in control of action.
[10] The concept was first termed "postural schema" to describe the disordered spatial representation of patients following damage to the parietal lobe of the brain.
[10] The term and definition first suggested by Head and Holmes has endured nearly a century of research with clarifications as more has become known about neuroscience and the brain.
[2]Neuroscientists Patrick Haggard and Daniel Wolpert have identified seven fundamental properties of the body schema.
A combination of sensory information, primarily tactile and visual, contributes to the representation of the limbs in space.
[2] Recent fMRI (functional Magnetic Resonance Imaging) studies confirm earlier results.
For example, the schema for feet and hands are coded by different regions of the brain, while the fingers are represented by a separate part entirely.
This simultaneous participation means there are combined representations within the body schema, which suggests the involvement of a process to translate primary information (e.g. visual, tactile, etc.)
Resolving these inter-sensory inconsistencies can result in interesting sensations, such as those experienced during the Rubber Hand Illusion.
The neuron has a tactile receptive field (responsive region on the body surface) typically on the face, arms, or hands.
Similar neuronal properties may also be important for the ability to incorporate external objects into the body schema, such as in tool use.
In some studies, attempts at understanding tool assimilation are used to argue for the existence of the extended body schema.
Subjects accustomed their eyes to a dark room and then were shown a brief (1 millisecond) flash of light, intending to produce an afterimage effect of their arms which they held out in front of them during the experiment.
Some research supports the claim that these two categories are purely distinct and do not intermingle, contrary to what the extended body schema theory describes.
Evidence for such is primarily found in subjects with unilateral neglect, such as in the case of E.D.S., who was a middle-aged man with right hemisphere brain damage.
The most famous case of this disorder is "IW", who lost all sensory input from below the neck, resulting in temporary paralysis.
IW requires constant attention to tasks to be able to complete them accurately, demonstrating how automatic and subconscious the process of integrating touch and proprioception into the body schema actually is.
Patients with this disorder make errors which result from confusion between adjacent body parts.
[23] A common theory posits that the afferent neurons, since deafferented due to amputation, typically remap to adjacent cortical regions within the brain.
Another facet of phantom limbs is that the efferent copy (motor feedback) responsible for reporting on position to the body schema does not attenuate quickly.
[9] In humans, body schema plays an important role in both simple and complex tool use, far beyond that of macaques.
[9] Recent research into the short term plasticity of the body schema used individuals without any prior training with tools.
