Conceptualizing functional neuroplasticity

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• Journal of Communication Disorders Volume 33, Issue 4, July–August 2000, Pages 345-356

• Conceptualizing functional neuroplasticity Author links open overlay panelJordan Grafman

• There are at least four major forms of functional neuroplasticity that can be studied in humans: homologous area adaptation, cross-modal reassignment, map expansion, and compensatory masquerade.

• Homologous area adaptation is the assumption of a particular cognitive process by a homologous region in the opposite hemisphere.

• Cross-modal reassignment occurs when structures previously devoted to processing a particular kind of sensory input now accepts input from a new sensory method.

• Map expansion is the enlargement of a functional brain region on the basis of performance.

• Compensatory masquerade is a novel allocation of a particular cognitive process to perform a task.

• mapping the functions of the human brain and in determining the knowledge, representational elements, and processes that are subserved by cognitive maps (Merzenich et al., 1996a).

• the brain appears to be composed of modular neural networks within which a defined representational unit is homogeneously represented. Such units may range from edge detectors used in visual processing (Gilbert, 1996) and stored in the occipital cortex to high-level plan representations used to guide behavior and stored in the prefrontal cortex (Grafman, 1995)

• function is usually shifted to another module in the homologous region of the opposite hemisphere; Chugani, Muller, & Chugani, 1996

• This crowding leads to a sparser representation of knowledge within the shifted module and increases the likelihood of dual-task interference when two tasks to be performed simultaneously involve adjacent “modules” in the cortex

• This form of neuroplastic change is reported less often in adults.

• an adolescent who had incurred a severe right parietal lobe brain injury as a young child (Levin et al., 1996)

• patient who experienced a severe stroke that destroyed almost the entire left hemisphere

• Cross-modal reassignment

• positron emission tomography and functional magnetic resonance imaging studies of tactile discrimination ability have shown that persons who became blind early in childhood, but tested as adults, have somatosensory input redirected into area V1 of the occipital cortex, whereas normal control participants do not show evidence of any V1 activation during the same task (Sadato et al., 1996).

• there are probably limitations to the feasibility of this form of neuroplasticity. For example, color processing cells in the occipital cortex are specialized for visual input and would be unlikely to accept other forms of input.

• Map expansion

• In two studies using two different techniques (transcranial magnetic stimulation and electroencephalography; Pascual-Leone, Grafman, & Hallett 1994, Zhuang et al. 1997), we demonstrated that implicit learning of a visuomotor sequence induced sensorimotor map expansion in the early stages of (implicit) learning. When learning became explicit, the cortical map size returned to baseline.

• this rapid enlargement of selected cortical maps can be persistent in individuals who develop or are trained in a particular skill that they need to use on a routine basis (Rosenzweig & Bennett, 1996).