Somatosensory cortical plasticity in adult humans revealed by magnetoencephalography.

Abstract

Microelectrode recordings in adult mammals have clearly demonstrated that somatosensory cortical maps reorganize following peripheral nerve injuries and functional modifications; however, such reorganization has never been directly demonstrated in humans. Using magnetoencephalography, we have been able to demonstrate the somatotopic organization of the hand area in normal humans with high spatial precision. Somatosensory cortical plasticity was detected in two adults who were studied before and after surgical separation of webbed fingers (syndactyly). The presurgical maps displayed shrunken and nonsomatotopic hand representations. Within weeks following surgery, cortical reorganization occurring over distances of 3-9 mm was evident, correlating with the new functional status of their separated digits. In contrast, no modification of the somatosensory map was observed months following transfer of a neurovascular skin island flap for sensory reconstruction of the thumb in two subjects in whom sensory transfer failed to occur.Understanding the presence, degree, and functional correlations for human cortical plasticity is of major significance for fundamental neuroscience as well as a potential aid in the diagnosis and rehabilitation of patients with peripheral and central nervous system injuries. That cortical maps can undergo reorganization in adult mammals has been demonstrated following a variety of peripheral sensory alterations including nerve transection (1-3), digital amputation (4,5) and syndactyly (6), and behavioral modification (7,8). Direct neurophysiological evidence for human somatosensory cortical plasticity, however, has never been demonstrated (9).Magnetoencephalography (MEG) is a noninvasive functional brain imaging technique that provides information regarding neuronal activity with high temporal and spatial resolution (10-14). Initial studies using MEG (10,12,14) demonstrated the somatotopy of the human somatosensory cortex, and present-day technology allows such functional maps to be defined with millimeter precision (14). We have been investigating the detailed functional organization of the hand area in normal adult humans and in patients with a variety of congenital and traumatic hand abnormalities. We report here evidence of adult human cortical plasticity, occurring over a time period of weeks to months following surgical correction of congenital syndactyly in two adult males. METHODSA 14-and a 37-channel biomagnetic recording system (Biomagnetic Technologies, San Diego) were used. The orientation of the subject's head in relation to the MEG recording probes was calculated using the sensor position indicator (SPI), a system of transmitters located on the dewars and receivers. affixed to a headband on the patient's head. Sensor locations were expressed using a head-based coordinate system whose origin was defined as the point of perpendicular intersection of the line extending from the nasion and the line connecting the penauricular points. The x, y, and z axes were the lines from t...

Functional Organization of Primary Somatosensory Cortex Depends on the Focus of Attention

“…For example, it has been reported that d1-d3 distances expand when patterned stimulation is delivered to digits 1, 3, and 5 compared to when these digits are stimulated in a random order (Braun et al, 2000a) and that d1-d5 distances expand when the intervening digits 2, 3, and 4 are anesthetized (Buchner et al, 1995 or when fingers conjoined by syndactly are separated by surgery (Mogilner et al, 1993). In addition, the strength of the cortical representation when multiple digits are stimulated concurrently is less than the sum of their individual representations (Liu et al, 2000), which suggests that digit representations are tuned by reciprocal interactions in agreement with findings reported by Mirabella et al (2001) for rat barrel neurons.…”

The Effect of Cervical Spine Manipulation on Postural Sway in Patients With Nonspecific Neck Pain

“…These changes are surprisingly rapid. Both human and primate studies have reported that changes in cortical activity take place within the first few weeks following injury (Merzenich et al, 1983;Mogilner et al, 1993) and that chronic changes begin within the first two months (Churchill, Muja, Myers, Besheer, & Garraghty, 1998). These changes take place in several forms including alteration of normal inhibition/excitation processes, atrophy of normal structures and formation of new connections .…”

Alteration of digital representations in somatosensory cortex in focal hand dystonia

“…Moreover, surgically joining two digits in monkeys resulted in a fused cortical receptive field for those two digits, 11,12 while surgical separation of digits in syndactylous Clinical Neuroscience 1111 2 3 4 5 6 7 8 9 10111 1 2 3 4 5 6 7 8 9 20111 1 2 3 4 5 6 7 8 9 30111 1 2 3 4 5 6 7 8 9 40111 1 2 3 4 5 6 7 8 9 50111 1 2 3 4 5 humans led to a separation of the cortical representational zones of the digits. 13 Similarly, Sterr et al 14,15 found that the cortical representation of the digits became topographically disordered in blind individuals who read Braille with three fingers simultaneously for many hours on a daily basis. Thus, extensive simultaneous stimulation of the digits and other types of prolonged, unusual types of sensory input can produce a use-dependent reorganization of digital receptive fields.…”