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Brain mapping of the upper limb muscles: a TMS study
NemoImage 11, Number 5, 2000, Part 2 of 2 Parts 1 DE al@
PHYSIOLOGY
Brain mapping of the upper limb muscles: a TMS study Patrizio Pasqualetti, F’lavia Pam-i, Paolo Maria Rossini AFaR-CRCCS Ospea!ale Fatebenefratelli
Isola Tiberina
The existence of multiple yet discrete effereru zones from primary motor cortex is now accepted to represent an essential organizational principle of this area in animal experimental models. Several reports from different research groups have reported that a particular movement can be elicited from separate MI regions, often several millimeters apart separate by non-responsive districts at least for the tested movement. The intracortical microstimulation is able to identify some segregated areas in MI triggering movements in shoulder, elbow, wrist and fingers. A large body of evidence challenge the hypothesis which suggests that control of the primate arm is like in a robotic hand having separate software channels, servo amplifiers and motors for each digit. On the other side, it suppotts the view that any movement is controlled by a network of neurons distributed throughout MI cortex. Moreover, such studies provide evidence oE -convergence of output from large, overlapping cortical territories onto single muscles; -divergence of output from any given cortical site to multiple muscles; -extensive horizontal interconnections between subregions within the MI. Previous studies never addressed in a comprehensive way the important problem of multiple representation of excitable areas for individual muscles as well as for different muscle combinations acting. Also, no previous reports dealt with the possible modifications of maps induced by simple changes in posture, like maintaining the forearm-hand supinated or prone. In the present report a detailed mapping of the motor output from more than 100 scalp sites for each hemisphere was carried out in combination with simultaneous MEP records from several hand, forearm, arm and shoulder muscles. Ten healthy vohmteers (4 males, 6 females, mean age 32.9 +/- 4.9 years) participated to this study. TMS was carried out via a @ure-of-eight coil delivering individual stimuli with a pseudo-random 0.15 c/see repetition rate. Subjects were wearing an elastic, transparent cup where the 121 sites forming the stimulation grid and anatomical landmarks (nasion, inion, vertex and external meati) were marked. Excitability threshold (Eth) was first established for one of the four tested hand muscles according with international standards. Then stimuli of 10% above the subject’s Eth were delivered to each of the sites of the stimulation grid. Montages were bipolar with a belly-tendon distribution from Abductor Digiti Minimi, First Dorsal Interosseous, Abductor Pollicis Brevis, Adductor Pollicis Brevis, Extensor Digitorum Communis, Extensor Indicis Proprius, Extensor Ulnaris Carpi, Extensor Radialis Carpi, Flexor Communis, Biceps, Triceps, Deltoid. For each stimulated scalp position, the median value of the responses has been determined. So the database included: 10 subjects x 121 scalp position = 121 rows, 2 parameters (latencies and amplitudes) x 12 muscles = 24 columns. Principal Component Analysis allowed finding out pools of muscles on the basis of their co-activation. Inter-subjects variability was taken into account. The homogeneity of the co-activation patterns across hemispheres and across the two hand postures were checked. The similarity of the representation of each muscle on the factorial space and on the stimulation grid was analyzed. The preliminary analysis allowed finding significant differences in muscles activation in some areas, whereas the pattern was homogeneous in others. In particular, in area 1 (hot spot for ADM) the muscle of hand and forearm resulted more represented and well distinguished in comparison with the arm muscles. In area 3 (more medial than the areal) cortical representation of proximal muscles is still well divided from the representation of distal muscles, but proximal muscles are less present. In area 5 (closer to Cz) muscles are pretty closed, probably because of a major representation of triceps, biceps and deltoid muscles. These results may suggest that all muscles taken into account in this study can be activated by stimulating several cortical points by means of Th4S. The cortical representation of the upper limb muscles is different for different group of muscles: distal muscles are more represented in number of elicited points and presented higher amplitude responses. In the map, it is possible to select areas where muscles are clearly separated and areas where cortical activation clearly shows an overlapping of responses of different muscles.
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PHYSIOLOGY
Brain mapping of the upper limb muscles: a TMS study Patrizio Pasqualetti, F’lavia Pam-i, Paolo Maria Rossini AFaR-CRCCS Ospea!ale Fatebenefratelli
Isola Tiberina
The existence of multiple yet discrete effereru zones from primary motor cortex is now accepted to represent an essential organizational principle of this area in animal experimental models. Several reports from different research groups have reported that a particular movement can be elicited from separate MI regions, often several millimeters apart separate by non-responsive districts at least for the tested movement. The intracortical microstimulation is able to identify some segregated areas in MI triggering movements in shoulder, elbow, wrist and fingers. A large body of evidence challenge the hypothesis which suggests that control of the primate arm is like in a robotic hand having separate software channels, servo amplifiers and motors for each digit. On the other side, it suppotts the view that any movement is controlled by a network of neurons distributed throughout MI cortex. Moreover, such studies provide evidence oE -convergence of output from large, overlapping cortical territories onto single muscles; -divergence of output from any given cortical site to multiple muscles; -extensive horizontal interconnections between subregions within the MI. Previous studies never addressed in a comprehensive way the important problem of multiple representation of excitable areas for individual muscles as well as for different muscle combinations acting. Also, no previous reports dealt with the possible modifications of maps induced by simple changes in posture, like maintaining the forearm-hand supinated or prone. In the present report a detailed mapping of the motor output from more than 100 scalp sites for each hemisphere was carried out in combination with simultaneous MEP records from several hand, forearm, arm and shoulder muscles. Ten healthy vohmteers (4 males, 6 females, mean age 32.9 +/- 4.9 years) participated to this study. TMS was carried out via a @ure-of-eight coil delivering individual stimuli with a pseudo-random 0.15 c/see repetition rate. Subjects were wearing an elastic, transparent cup where the 121 sites forming the stimulation grid and anatomical landmarks (nasion, inion, vertex and external meati) were marked. Excitability threshold (Eth) was first established for one of the four tested hand muscles according with international standards. Then stimuli of 10% above the subject’s Eth were delivered to each of the sites of the stimulation grid. Montages were bipolar with a belly-tendon distribution from Abductor Digiti Minimi, First Dorsal Interosseous, Abductor Pollicis Brevis, Adductor Pollicis Brevis, Extensor Digitorum Communis, Extensor Indicis Proprius, Extensor Ulnaris Carpi, Extensor Radialis Carpi, Flexor Communis, Biceps, Triceps, Deltoid. For each stimulated scalp position, the median value of the responses has been determined. So the database included: 10 subjects x 121 scalp position = 121 rows, 2 parameters (latencies and amplitudes) x 12 muscles = 24 columns. Principal Component Analysis allowed finding out pools of muscles on the basis of their co-activation. Inter-subjects variability was taken into account. The homogeneity of the co-activation patterns across hemispheres and across the two hand postures were checked. The similarity of the representation of each muscle on the factorial space and on the stimulation grid was analyzed. The preliminary analysis allowed finding significant differences in muscles activation in some areas, whereas the pattern was homogeneous in others. In particular, in area 1 (hot spot for ADM) the muscle of hand and forearm resulted more represented and well distinguished in comparison with the arm muscles. In area 3 (more medial than the areal) cortical representation of proximal muscles is still well divided from the representation of distal muscles, but proximal muscles are less present. In area 5 (closer to Cz) muscles are pretty closed, probably because of a major representation of triceps, biceps and deltoid muscles. These results may suggest that all muscles taken into account in this study can be activated by stimulating several cortical points by means of Th4S. The cortical representation of the upper limb muscles is different for different group of muscles: distal muscles are more represented in number of elicited points and presented higher amplitude responses. In the map, it is possible to select areas where muscles are clearly separated and areas where cortical activation clearly shows an overlapping of responses of different muscles.
S7%