Reorganization of cortical blood flow and transcranial magnetic stimulation maps in human subjects after upper limb amputation

Abstract

1. Two complimentary techniques were used to study cortical function in six human upper limb amputees: positron emission tomographic (PET) measurements of regional cerebral blood flow (rCBF) were made in subjects during limb movements to study activation of the primary motor (M1), primary somatosensory (S1), and association cortices; and electromyographic responses to transcranial magnetic stimulation (TMS) were measured in proximal upper limb muscles to assess the excitability of corticospinal neurons in subjects at rest. 2. To explore possible cortical mechanisms governing the phantom limb phenomenon, PET and TMS findings were compared between subjects with acquired, traumatic upper limb amputations (n = 3), in whom phantom limb symptoms were prominent, and congenital upper limb amputees (n = 3) without phantom limbs. 3. Paced shoulder movements were associated with significant blood flow increases in the contralateral M1/S1 cortex of both groups of amputees. In traumatic amputees, these increases were present over a wider area and were of significantly greater magnitude in the partially deafferented cortex contralateral to the amputation. In congenital amputees blood flow increases were also present over a wider area in the partially deafferented M1/S1 cortex, but their magnitude was not significantly different from that in the normally afferented M1/S1 cortex. 4. Abnormal blood flow increases also were present in the partially deafferented M1/S1 cortex of traumatic amputees during movement of the ipsilateral, intact arm. Abnormal ipsilateral M1/S1 responses were not present during movement of the intact arm in the congenital group. 5. TMS studies showed that the abnormal blood flow increases in the partially deafferented M1 cortex of traumatic amputees were associated with increased corticospinal excitability.(ABSTRACT TRUNCATED AT 250 WORDS)

Cortical reorganization and phantom phenomena in congenital and traumatic upper-extremity amputees

“…In contrast, Cohen et al (1991) reported that only the traumatic amputees showed enhanced reactivity in the musculature close to the amputation site, but this did not occur in a congenital amputee. The findings of Kew et al (1994) are consistent with those of the latter experiment. Kew et al studied three traumatic and three congenital amputees using positron emission tomography and transcranial magnetic stimulation during paced shoulder movements on the intact and the amputation side.…”

More than skin deep: Body representation beyond primary somatosensory cortex

“…Similarly, subjective experiences of phantom limbs are not strongly related to sensory thresholds or tactile acuity on the stump (Hunter, Katz, & Davis, 2005). Furthermore, Kew et al (1994) found abnormal increases in the posterior parietal cortex activity related to movements of the phantom arm. Furthermore, while ablation of SI has remarkably little effect on phantom limbs (White & Sweet, 1969), some authors have reported that lesions of the posterior parietal cortex can suppress the experience of phantom limbs (Berlucchi & Aglioti, 1997).…”

Modulation of motor cortex excitability after upper limb immobilization

“…Learning new motor skills (Pascual-Leone et al, 1995) and performing skilled motor activities result in an expansion of the representation of the muscles involved in the task. Complete long term sensorimotor deafferentation, as in the case of limb amputation (Chen et al, 1998;Cohen et al, 1991;Kew et al, 1994;Ridding and Rothwell, 1997;Wu and Kaas, 1999) and peripheral nerve lesions (Rijntjes et al, 1997;Tinazzi et al, 1998), as well as short term deafferentation secondary to ischemic nerve block (Brasil-Neto et al, 1993;Ridding and Rothwell, 1997;Ziemann et al, 1998a;Ziemann et al, 1998b), result in an expansion of the surrounding representations.…”