Functional magnetic resonance studies of the reorganization of the human hand sensorimotor area after unilateral brain injury in the perinatal period.

Abstract

Functional magnetic resonance ging was used to map the hand sensorimotor area of hemiparetic adolescents and young adults who had suffered unilateral brain damage in the perinatal period. Unlike normal subjects, who exhibit cortical activation primarily contralateral to voluntary finger movements, the hemaretic patients' intact hemispheres were equally activated by contralateral and ipsilateral finger movements. Our fidings are consistent with previous clinical observations and animal experiments which suggest that the immature brain is able to reorganize in response to focal injury.Many observations suggest that the immature human brain is characterized by "plasticity": i.e., it is capable of major functional reorganization in response to external and internal stimuli. For example, children will recover language skills after sustaining a large insult or even hemispherectomy on the speech-dominant side if the damage occurs before age 7 or 8 (1). Similarly, if a child with strabismus is forced to use the squinting eye by patching of the good eye before about age 7, permanent visual loss in the squinting eye (amblyopia) can be prevented (2, 3). The sensorimotor system also demonstrates plasticity. Children with large unilateral brain lesions can learn to reach out and grasp an object and can walk, although with a limp (4). Movements of the paretic hand in these children are often accompanied by "mirror" movements on the opposite side (5, 6). Such parallel movements are much more prominent when brain injury occurs before 1 year of age (6). These observations suggest that motor function might be represented in the hemisphere ipsilateral to the weak hand if injury is incurred early in life.Similar effects have been found in animal models: e.g., the reaction of the rodent motor system to postnatal hemispherectomy. In this model, it has been shown that the remaining hemisphere develops a new, uncrossed corticospinal tract to the ipsilateral spinal cord in addition to the usual crossed one (7). Huttenlocher et al. (8,9) have succeeded in making separate cortical maps of the neurons forming the aberrant (uncrossed) and normal (crossed) tracts. The neurons which are "recruited" to form the uncrossed tract are found in the same areas as the usual "crossed" neurons, as well as in the adjacent cortex. Thus, these cortical mapping experiments suggest that a limited population of multipotential neurons might be involved in brain plasticity. The mechanisms of neural reorganization in the human brain are not well understood (10) but may involve the unmasking of existing pathways (11, 12), competition for synaptic space (13), or axonal migration and sprouting along chemical gradients (14).Although ample clinical observations (1-7) and animal experiments (8,9,15) suggest that the human brain demonstrates plasticity, there are few studies that provide brain mapping evidence for cortical reorganization after motorcortex lesions. A single case report utilizing magnetoencephalography suggested reorganization in the somatosenso...

Functional Recovery and Enhanced Corticofugal Plasticity after Unilateral Pyramidal Tract Lesion and Blockade of Myelin-Associated Neurite Growth Inhibitors in Adult Rats

“…After unilateral neonatal pyramidotomy in rodents, corticoefferent fibers from the same side as the lesion were found to cross the midline to form new connections with medullary nuclei and to descend to spinal cord levels . Evidence that new neural connections occur after perinatal brain damage in children is supported by several clinical studies (Farmer et al, 1991;C arr et al, 1993;C ao et al, 1994). Structural neuroplasticity is thought to play an essential role in recovery of function, because animals sustaining C NS lesions at a young age are known to recover much better than those sustaining similar lesions at maturity (Kennard, 1936(Kennard, , 1938Whishaw and Kolb, 1988;Armand and Kably, 1993).…”

Intraoperative validation of functional magnetic resonance imaging and cortical reorganization patterns in patients with brain tumors involving the primary motor cortex

“…The recovery of motor function, which indicated the complexity and interplay of neuronal activity among different motor areas, led to the study of "functional reorganization" and "plasticity" in patients with stroke, [10,46] brain injury, [8] and brain tumors. [42] Studying six patients after their recovery from hemiplegic stroke by using PET, Chollet, et al, [10] demonstrated bilateral activation (rCBF increase) of MII, SMA, and insula during movement of the recovered fingers.…”

Visuotactile interactions in the congenitally acallosal brain: Evidence for early cerebral plasticity

“…This suggests that further mechanisms must be involved, e.g. an increased use of ipsilateral pathways that then connect to commissural systems (Cao et al, 1994;Chiarello, 1980). Furthermore, bimodal cells, which integrate information from different sensory modalities (reviewed by Stein & Stanford, 2008), are not only found in cortical structures (e.g.…”

“…It is well-known that developmental malformations may affect cerebral functioning in several ways (Cao, Vikingstad, Huttenlocher, Towle, & Levin, 1994;Hicks & D'Amato, 1970). The crossmodal congruency task also allowed us to compare performance between AgCC patients and controls for cases in which no hemispheric transfer was necessary to test whether the absence of the corpus callosum alters information processing within one hemisphere.…”