Effects of Red Nucleus Microstimulation on the Locomotor Pattern and Timing in the Intact Cat: A Comparison With the Motor Cortex

1999 ◽  
Vol 81 (5) ◽  
pp. 2297-2315 ◽  
Author(s):  
Marie-Josée Rho ◽  
Sylvain Lavoie ◽  
Trevor Drew
Keyword(s):  
Motor Cortex ◽  
Red Nucleus ◽  
Emg Activity ◽  
Cycle Duration ◽  
Step Cycle ◽  
Rubrospinal Tract ◽  
Locomotor Pattern ◽  
Train Duration ◽  
Flexor Muscles ◽  
Cathodal Current

Effects of red nucleus microstimulation on the locomotor pattern and timing in the intact cat: a comparison with the motor cortex. To determine the extent to which the rubrospinal tract is capable of modifying locomotion in the intact cat, we applied microstimulation (cathodal current, 330 Hz; pulse duration 0.2 ms; maximal current, 25 μA) to the red nucleus during locomotion. The stimuli were applied either as short trains (33 ms) of impulses to determine the capacity of the rubrospinal tract to modify the level of electromyographic (EMG) activity in different flexors and extensors at different phases of the step cycle or as long trains (200 ms) of pulses to determine the effect of the red nucleus on cycle timing. Stimuli were also applied with the cat at rest (33-ms train). This latter stimulation evoked short-latency (average = 11.8–19.0 ms) facilitatory responses in all of the physiological flexor muscles of the forelimb that were recorded; facilitatory responses were also common in the elbow extensor, lateral head of triceps but were rare in the physiological wrist and digit extensor, palmaris longus. Responses were still evoked in most muscles when the current was decreased to near threshold (3–10 μA). Stimulation during locomotion with the short trains of stimuli evoked shorter-latency (average = 6.0–12.5 ms) facilitatory responses in flexor muscles during the swing phase of locomotion and, except in the case of the extensor digitorum communis, evoked substantially smaller responses in stance. The same stimuli also evoked facilitatory responses in the extensor muscles during swing and produced more complex effects involving both facilitation and suppression in stance. Increasing the duration of the train to 200 ms modified the amplitude and duration of the EMG activity of both flexors and extensors but had little significant effect on the cycle duration. In contrast, whereas stimulation of the motor cortex with short trains of stimuli during locomotion had very similar effects to that of the red nucleus, increasing the train duration to 200 ms frequently produced a marked reset of the step cycle by curtailing stance and initiating a new period of swing. The results suggest that whereas both the motor cortex and the red nucleus have access to the interneuronal circuits responsible for controlling the structure of the EMG activity in the step cycle, only the motor cortex has access to the circuits responsible for controlling cycle timing.

Contribution of the Motor Cortex to the Structure and the Timing of Hindlimb Locomotion in the Cat: A Microstimulation Study

2005 ◽  
Vol 94 (1) ◽  
pp. 657-672 ◽  
Author(s):  
Frédéric Bretzner ◽  
Trevor Drew
Keyword(s):  
Motor Cortex ◽  
Muscle Activity ◽  
Pyramidal Tract ◽  
Cycle Duration ◽  
Step Cycle ◽  
Standard Glass ◽  
Level Of Activity ◽  
Flexor Muscles ◽  
Multijoint Movements ◽  
Stimulation Of

We used microstimulation to examine the contribution of the motor cortex to the structure and timing of the hindlimb step cycle during locomotion in the intact cat. Stimulation was applied to the hindlimb representation of the motor cortex in 34 sites in three cats using either standard glass-insulated microelectrodes (16 sites in 1 cat) or chronically implanted microwire electrodes (18 sites in 2 cats). Stimulation at just suprathreshold intensities with the cat at rest produced multijoint movements at a majority of sites (21/34, 62%) but evoked responses restricted to a single joint, normally the ankle, at the other 13/34 (38%) sites. Stimulation during locomotion generally evoked larger responses than the same stimulation at rest and frequently activated additional muscles. Stimulation at all 34 sites evoked phase-dependent responses in which stimulation in swing produced transient increases in activity in flexor muscles while stimulation during stance produced transient decreases in activity in extensors. Stimulation with long (200 ms) trains of stimuli in swing produced an increased level of activity and duration of flexor muscles without producing changes in cycle duration. In contrast, stimulation during stance decreased the duration of the extensor muscle activity and initiated a new and premature period of swing, resetting the step cycle. Stimulation of the pyramidal tract in two of these three cats as well as in two additional ones produced similar effects. The results show that the motor cortex is capable of influencing hindlimb activity during locomotion in a similar manner to that seen for the forelimb.

Discharge Characteristics of Neurons in the Red Nucleus During Voluntary Gait Modifications: A Comparison with the Motor Cortex

2002 ◽  
Vol 88 (4) ◽  
pp. 1791-1814 ◽  
Author(s):  
Sylvain Lavoie ◽  
Trevor Drew
Keyword(s):  
Motor Cortex ◽  
Cortical Neurons ◽  
Red Nucleus ◽  
Receptive Fields ◽  
Maximal Activity ◽  
Swing Phase ◽  
Emg Activity ◽  
Step Cycle ◽  
Step Over ◽  
Increased Activity

We have examined the contribution of the red nucleus to the control of locomotion in the cat. Neuronal activity was recorded from 157 rubral neurons, including identified rubrospinal neurons, in three cats trained to walk on a treadmill and to step over obstacles attached to the moving belt. Of 72 neurons with a receptive field confined to the contralateral forelimb, 66 were phasically active during unobstructed locomotion. The maximal activity of the majority of neurons (59/66) was centered around the swing phase of locomotion. Slightly more than half of the neurons (36/66) were phasically activity during both swing and stance. In addition, some rubral neurons (14/66) showed multiple periods of phasic activity within the swing phase of the locomotor cycle. Periods of phasic discharge temporally coincident with the swing phase of the ipsilateral limb were observed in 7/66 neurons. During voluntary gait modifications, most forelimb-related neurons (70/72) showed a significant increase in their discharge activity when the contralateral limb was the first to step over the obstacle (lead condition). Maximal activity in nearly all cells (63/70) was observed during the swing phase, and 23/63 rubral neurons exhibited multiple increases of activity during the modified swing phase. A number of cells (18/70) showed multiple periods of increased activity during swing and stance. Many of the neurons (35/63, 56%) showed an increase in activity at the end of the swing phase; this period of activity was temporally coincident with the period of activity in wrist dorsiflexors, such as the extensor digitorum communis. A smaller proportion of neurons with receptive fields restricted to the hindlimbs showed similar characteristics to those observed in the population of forelimb-related neurons. The overall characteristics of these rubral neurons are similar to those that we obtained previously from pyramidal tract neurons recorded from the motor cortex during an identical task. However, in contrast to the results obtained in the rubral neurons, most motor cortical neurons showed only one period of increased activity during the step cycle. We suggest that both structures contribute to the modifications of the pattern of EMG activity that are required to produce the change in limb trajectory needed to step over an obstacle. However, the results suggest an additional role for the red nucleus in regulating intra- and interlimb coordination.

Plasticity in the Distribution of the Red Nucleus Output to Forearm Muscles After Unilateral Lesions of the Pyramidal Tract

2000 ◽  
Vol 83 (5) ◽  
pp. 3147-3153 ◽  
Author(s):  
Abderraouf Belhaj-Saïf ◽  
Paul D. Cheney
Keyword(s):  
Pyramidal Tract ◽  
Red Nucleus ◽  
Emg Activity ◽  
Motor Impairments ◽  
Forearm Muscles ◽  
Extensor Muscles ◽  
Flexor Muscles ◽  
Lesion Method ◽  
Stimulus Triggered Averaging ◽  
Suppression Effects

It has been hypothesized that the magnocellular red nucleus (RNm) contributes to compensation for motor impairments associated with lesions of the pyramidal tract. To test this hypothesis, we used stimulus triggered averaging (StTA) of electromyographic (EMG) activity to characterize changes in motor output from the red nucleus after lesions of the pyramidal tract. Three monkeys were trained to perform a reach and prehension task. EMG activity was recorded from 11 forearm muscles including one elbow, five wrist, and five digit muscles. Microstimulation (20 μA at 20 Hz) was delivered throughout the movement task to compute StTAs. Two monkeys served as controls. In a third monkey, 65% of the left pyramidal tract had been destroyed by an electrolytic lesion method five years before recording. The results demonstrate a clear pattern of postlesion reorganization in red nucleus–mediated output effects on forearm muscles. The normally prominent extensor preference in excitatory output from the RNm (92% in extensors) was greatly diminished in the lesioned monkey (59%). Similarly, suppression effects, which are normally much more prominent in flexor than in extensor muscles (90% in flexors), were also more evenly distributed after recovery from pyramidal tract lesions. Because of the limited excitatory output from the RNm to flexor muscles that normally exists, loss of corticospinal output would leave control of flexors particularly weak. The changes in RNm organization reported in this study would help restore function to flexor muscles. These results support the hypothesis that the RNm is capable of reorganization that contributes to the recovery of forelimb motor function after pyramidal tract lesions.

Comparison of the Effect of Intrathecal Administration of Clonidine and Yohimbine on the Locomotion of Intact and Spinal Cats

2001 ◽  
Vol 85 (6) ◽  
pp. 2516-2536 ◽  
Author(s):  
Nathalie Giroux ◽  
Tomás A. Reader ◽  
Serge Rossignol
Keyword(s):  
Acid Methyl Ester ◽  
Intrathecal Administration ◽  
Cycle Duration ◽  
Descending Pathways ◽  
Step Cycle ◽  
Locomotor Pattern ◽  
Before And After ◽  
Spontaneous Expression ◽  
High Doses ◽  
Treadmill Locomotion

Several studies have shown that noradrenergic mechanisms are important for locomotion. For instance, L-dihydroxyphenylalanine (L-DOPA) can initiate “fictive” locomotion in immobilized acutely spinalized cats and α2-noradrenergic agonists, such as 2,6,-dichloro- N-2-imidazolidinylid-enebenzenamine (clonidine), can induce treadmill locomotion soon after spinalization. However, the activation of noradrenergic receptors may be not essential for the basic locomotor rhythmicity because chronic spinal cats can walk with the hindlimbs on a treadmill in the absence of noradrenergic stimulation because the descending pathways are completely severed. This suggests that locomotion, in intact and spinal conditions, is probably expressed and controlled through different neurotransmitter mechanisms. To test this hypothesis, we compared the effect of the α2 agonist, clonidine, and the antagonist (16α, 17α)-17-hydroxy yohimbine-16-carboxylic acid methyl ester hydrochloride (yohimbine), injected intrathecally at L3–L4before and after spinalization in the same cats chronically implanted with electrodes to record electromyograms (EMGs). In intact cats, clonidine (50–150 μg/100 μl) modulated the locomotor pattern slightly causing a decrease in duration of the step cycle accompanied with some variation of EMG burst amplitude and duration. In the spinal state, clonidine could trigger robust and sustained hind limb locomotion in the first week after the spinalization at a time when the cats were paraplegic. Later, after the spontaneous recovery of a stable locomotor pattern, clonidine prolonged the cycle duration, increased the amplitude and duration of flexor and extensor bursts, and augmented the foot drag at the onset of swing. In intact cats, yohimbine at high doses (800–1600 μg/100 μl) caused major walking difficulties characterized by asymmetric stepping, stumbling with poor lateral stability, and, at smaller doses (400 μg/100 μl), only had slight effects such as abduction of one of the hindlimbs and the turning of the hindquarters to one side. After spinalization, yohimbine had no effect even at the largest doses. These results indicate that, in the intact state, noradrenergic mechanisms probably play an important role in the control of locomotion since blocking the receptors results in a marked disruption of walking. In the spinal state, although the receptors are still present and functional since they can be activated by clonidine, they are seemingly not critical for the spontaneous expression of spinal locomotion since their blockade by yohimbine does not impair spinal locomotion. It is postulated therefore that the expression of spinal locomotion must depend on the activation of other types of receptors, probably related to excitatory amino acids.

Patterns of facilitation and suppression of antagonist forelimb muscles from motor cortex sites in the awake monkey

1985 ◽  
Vol 53 (3) ◽  
pp. 805-820 ◽  
Author(s):  
P. D. Cheney ◽  
E. E. Fetz ◽  
S. S. Palmer
Keyword(s):  
Motor Cortex ◽  
Single Cells ◽  
Emg Activity ◽  
Detectable Effect ◽  
Onset Latency ◽  
Inhibitory Effects ◽  
Extensor Muscles ◽  
Flexor Muscles ◽  
Forelimb Muscles ◽  
The Mean

Patterns of excitatory and inhibitory effects were produced in antagonistic forelimb muscles by single intracortical microstimuli (S-ICMS) applied to motor cortex sites in macaque monkeys performing ramp-and-hold wrist movements. Stimulus-triggered averages (stimulus-TAs) of rectified electromyographic (EMG) activity revealed poststimulus facilitation and/or suppression in identified flexor and extensor muscles of the wrist and fingers. At 22 cortical sites the action potentials of single cells were also recorded and used to compute spike-triggered averages (spike-TAs) of covarying muscles. The set of muscles activated during the movement in which the cell was active are referred to here as "agonists"; those muscles active during wrist movement in the opposite direction are called "antagonists." (At sites where cells were not isolated the muscles showing poststimulus facilitation were called agonists.) Poststimulus effects in agonist muscles typically consisted of facilitation in a subset of the agonists. For 48 sites from which poststimulus effects were tested on both flexors and extensors, the following combinations of effects were observed: 1) pure facilitation of agonist muscles with no effect on antagonists; 2) facilitation of both agonists and antagonists; 3) facilitation of agonist muscles with reciprocal suppression of antagonists; 4) "mixed" facilitation and suppression of synergist muscles; and 5) pure suppression of some muscles with no effect on their antagonists. The suppression effects appeared most commonly in flexor muscles; conversely, facilitation was generally stronger in extensors. Cortical sites eliciting pure suppression of flexor muscles with no facilitation of extensor muscles were found in two monkeys. These purely suppressive effects were observed not only in stimulus-TAs but also in spike-TAs computed from single cells at these sites. Some of these cells increased their activity during wrist extension (but had no detectable effect on the extensor muscles); others discharged during flexion. Several observations suggest that the cortically evoked suppression is mediated by polysynaptic relays. The mean onset latency of the postspike suppression (7.4 ms) produced by inhibitory cells was longer than the mean onset latency of postspike facilitation (6.7 ms) produced by CM cells. Similarly, the mean onset latency of poststimulus suppression (8.9 ms) was longer than that of poststimulus facilitation (8.0 ms). Moreover, suppression was usually weaker than facilitation in the spike-TAs, as well as in stimulus-TAs compiled for the same stimulus intensity.(ABSTRACT TRUNCATED AT 400 WORDS)

Motor cortical activity during voluntary gait modifications in the cat. I. Cells related to the forelimbs

1993 ◽  
Vol 70 (1) ◽  
pp. 179-199 ◽  
Author(s):  
T. Drew
Keyword(s):  
Phase I ◽  
Phase Ii ◽  
Stance Phase ◽  
Discharge Frequency ◽  
Emg Activity ◽  
Recording Site ◽  
Step Cycle ◽  
Flexor Muscles ◽  
Gait Modification ◽  
Step Over

1. The discharge patterns of 91 identified pyramidal tract neurons (PTNs), located within the forelimb region of area 4 of the cat motor cortex, were recorded during the voluntary modifications of gait needed to step over obstacles attached to a moving treadmill belt. Recordings were made simultaneously from flexor and extensor muscles acting around the shoulder, elbow, wrist, and digits of the forelimb contralateral to the recording site. 2. Analysis of the changes in electromyographic (EMG) activity during the gait modification showed increases in the activity of most flexor muscles of the shoulder and elbow, as well as in the wrist and digit dorsiflexors, when the contralateral forelimb was the first to pass over the obstacle. This period of augmented activity could be subdivided into two parts: one associated with the initial flexion of the limb that was needed to bring it above and over the obstacle (phase I), and the second associated with increased wrist dorsiflexor muscle activity before foot contact (phase II). 3. The discharge frequency of a total of 57/91 (63%) of the recorded PTNs was significantly increased during the gait modification when the limb contralateral to the recording site was the first to step over the obstacle; six of these neurons also showed a significant decrease in their discharge in a different part of the step cycle. In a further 21/91 (23%) neurons, discharge frequency was only decreased, whereas the remaining 13/91 (14%) PTNs showed similar patterns of activity both during control walking and during the gait modifications. 4. Most of those neurons (47/57) in which significant increases in firing frequency were observed, discharged maximally during the period of increased activity of the physiological flexor muscles. Twenty-three of these cells (23/47) discharged maximally in phase I, and 12 (12/47) in phase II. A third population of PTNS (12/47) started to increase their discharge in the stance phase of the step cycle immediately preceding the modified cycle. Seven (7/57) PTNs increased their discharge during the stance phase of the modified cycle, and the remaining three could not be classified as being preferentially related to any one part of the step cycle. 5. The frequency modulation of 41/57 PTNs was less when the leg contralateral to the recording site was the second to encounter the obstacle. In many neurons there was also an appreciable change in the time in the step cycle that peak discharge occurred. These changes in amplitude and timing paralleled the changes observed in the temporal relationships of the muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution and Characteristics of Poststimulus Effects in Proximal and Distal Forelimb Muscles From Red Nucleus in the Monkey

1998 ◽  
Vol 79 (4) ◽  
pp. 1777-1789 ◽  
Author(s):  
Abderraouf Belhaj-Saïf ◽  
Jennifer Hill Karrer ◽  
Paul D. Cheney
Keyword(s):  
Functional Organization ◽  
Red Nucleus ◽  
Muscle Synergy ◽  
Reaching Movements ◽  
Emg Activity ◽  
Hand Muscles ◽  
Extensor Muscles ◽  
Flexor Muscles ◽  
Forelimb Muscles ◽  
Intrinsic Hand Muscles

Belhaj-Saı̈f, Abderraouf, Jennifer Hill Karrer, and Paul D. Cheney. Distribution and characteristics of poststimulus effects in proximal and distal forelimb muscles from red nucleus in the monkey. J. Neurophysiol. 79: 1777–1789, 1998. We used stimulus-triggered averaging (StTA) of electromyographic (EMG) activity to investigate two major questions concerning the functional organization of the magnocellular red nucleus (RNm) for reaching movements in the macaque monkey. The first is whether the clear preference toward facilitation of extensor muscles we have reported in previous studies for distal (wrist and digit) forelimb muscles also exists for proximal muscles (shoulder and elbow). The second question is whether distal and proximal muscles may be cofacilitated from RNm suggesting the representation of functional muscle synergies for coordinated reaching movements. Two monkeys were trained to perform a prehension task requiring multijoint coordination of the forelimb. EMG activity was recorded from 24 forelimb muscles including 5 shoulder, 7 elbow, 5 wrist, 5 digit, and 2 intrinsic hand muscles. Microstimulation (20 μA at 20 Hz) was delivered throughout the movement task. From 137 microstimulation sites in the RNm, a total of 977 poststimulus effects was obtained including 733 poststimulus facilitation effects (PStF) and 244 poststimulus suppression effects (PStS). Of the PStF effects, 58% were obtained from distal muscles; 42% from proximal muscles. Digit muscles were more frequently facilitated (35%) than the wrist, elbow, or shoulder muscles (20, 24, and 18%, respectively). The intrinsic hand muscles were infrequently facilitated (3%). At all joints tested, PStF was more common in extensor muscles than flexor muscles. This extensor preference was very strong for shoulder (85%), wrist (85%), and digit muscles (94%) and weaker for elbow muscles (60%). Of the PStS effects, 65% were in distal muscles and 35% in proximal muscles. Interestingly, the flexor muscles were more frequently inhibited from RNm than extensor muscles. At 72% of stimulation sites, at least two muscles were facilitated. The majority of these sites (61%) cofacilitated both proximal and distal muscles. At the remaining sites (39%), PStF was observed in either the proximal (17%) or distal muscles (22%). Facilitation most often involved combinations of shoulder, elbow, and distal muscles (30%) or shoulder and distal muscles (26%). Only rarely were intrinsic hand muscles part of the total muscle synergy. Our results show that the RNm 1) controls both proximal and distal muscles but the strength of influence is biased toward distal muscles, 2) preferentially controls extensor muscles not only at distal forelimb joints but also at proximal joints, and 3) output zones cofacilitate synergies of proximal and distal muscles involved in the control of forelimb reaching movements.

On the Potential Role of the Corticospinal Tract in the Control and Progressive Adaptation of the Soleus H-Reflex During Backward Walking

2005 ◽  
Vol 94 (2) ◽  
pp. 1133-1142 ◽  
Author(s):  
Roth-Visal Ung ◽  
Marie-Andrée Imbeault ◽  
Christian Ethier ◽  
Laurent Brizzi ◽  
Charles Capaday
Keyword(s):  
Motor Cortex ◽  
Large Amplitude ◽  
Corticospinal Tract ◽  
Motor Evoked Potentials ◽  
Conditioning Stimulus ◽  
H Reflex ◽  
Emg Activity ◽  
Step Cycle ◽  
Voluntary Activity ◽  
Backward Walking

When untrained subjects walk backward on a treadmill, an unexpectedly large amplitude soleus H-reflex occurs in the midswing phase of backward walking. We hypothesized that activity in the corticospinal tract (CST) during midswing depolarizes the soleus α-motoneurons subliminally and thus brings them closer to threshold. To test this hypothesis, transcranial magnetic stimulation (TMS) was applied to the leg area of the motor cortex (MCx) during backward walking. Motor-evoked potentials (MEPs) were recorded from the soleus and tibialis anterior (TA) muscles in untrained subjects at different phases of the backward walking cycle. We reasoned that if soleus MEPs could be elicited in midswing, while the soleus is inactive, this would be strong evidence for increased postsynaptic excitability of the α-motoneurons. In the event, we found that in untrained subjects, despite the presence of an unexpectedly large H-reflex in midswing, no soleus MEPs were observed at that time. The soleus MEPs were in phase with the soleus electromyographic (EMG) activity during backward walking. Soleus MEPs increased more rapidly as a function of the EMG activity during voluntary activity than during backward walking. Furthermore, a conditioning stimulus to the motor cortex facilitated the soleus H-reflex at rest and during voluntary plantarflexion but not in the midswing phase of backward walking. With daily training at walking backward, the time at which the H-reflex began to increase was progressively delayed until it coincided with the onset of soleus EMG activity, and its amplitude was considerably reduced compared with its value on the first experimental day. By contrast, no changes were observed in the timing or amplitude of soleus MEPs with training. Taken together, these observations make it unlikely that the motor cortex via the CST is involved in control of the H-reflex during the backward step cycle of untrained subjects nor in its progressive adaptation with training. Our observations raise the possibility that the large amplitude of H-reflex in untrained subjects and its adaptation with training are mainly due to control of presynaptic inhibition of Ia-afferents by other descending tracts.

Properties of Primary Motor Cortex Output to Forelimb Muscles in Rhesus Macaques

2004 ◽  
Vol 92 (5) ◽  
pp. 2968-2984 ◽  
Author(s):  
Michael C. Park ◽  
Abderraouf Belhaj-Saïf ◽  
Paul D. Cheney
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Rhesus Macaques ◽  
Red Nucleus ◽  
Macaque Monkey ◽  
Emg Activity ◽  
Reach To Grasp ◽  
Distal Muscle ◽  
Forelimb Muscles ◽  
Multijoint Movements

Stimulus-triggered averaging (StTA) of electromyographic (EMG) activity from 24 simultaneously recorded forelimb muscles was used to investigate properties of primary motor cortex (M1) output in the macaque monkey. Two monkeys were trained to perform a reach-to-grasp task requiring multijoint coordination of the forelimb. EMG activity was recorded from 24 forelimb muscles including 5 shoulder, 7 elbow, 5 wrist, 5 digit, and 2 intrinsic hand muscles. Microstimulation (15 μA at 15 Hz) was delivered throughout the movement task. From 297 stimulation sites in M1, a total of 2,079 poststimulus effects (PStE) were obtained including 1,398 poststimulus facilitation (PStF) effects and 681 poststimulus suppression (PStS) effects. Of the PStF effects, 60% were in distal and 40% in proximal muscles; 43% were of extensors and 47% flexors. For PStS, the corresponding numbers were 55 and 45% and 36 and 55%, respectively. M1 output effects showed extensive cofacilitation of proximal and distal muscles (96 sites, 42%) including 47 sites that facilitated at least one shoulder, elbow, and distal muscle, 45 sites that facilitated an elbow muscle and a distal muscle, and 22 sites that facilitated at least one muscle at all joints. The muscle synergies represented by outputs from these sites may serve an important role in the production of coordinated, multijoint movements. M1 output effects showed many similarities with red nucleus output although red nucleus effects were generally weaker and showed a strong bias toward facilitation of extensor muscles and a greater tendency to facilitate synergies involving muscles at noncontiguous joints.

Postnatal Development of the Motor Representation in Primary Motor Cortex

2000 ◽  
Vol 84 (5) ◽  
pp. 2582-2594 ◽  
Author(s):  
Samit Chakrabarty ◽  
John H. Martin
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Muscle Tone ◽  
Stimulus Frequency ◽  
Emg Activity ◽  
Postnatal Life ◽  
Motor Representation ◽  
Somatotopic Organization ◽  
Train Duration ◽  
Elbow Movement

The purpose of this study was to examine when the muscles and joints of the forelimb become represented in primary motor cortex (M1) during postnatal life and how local representation patterns change. We examined these questions in cats that were anesthetized (45–90 days, n = 14; adults, n = 3) and awake ( n = 4; 52–86 days). We used intracortical microstimulation (45 ms duration train, 330 Hz, 0.2-ms balanced biphasic pulses, with a leading cathodic pulse; up to 100 μA). In young animals (less than day 70), we also used stimulus trains and pulses that could produce greater temporal summation (up to 200-ms train duration, down to 143-Hz stimulus frequency, up to 0.8-ms pulse width). Anesthetized animals were areflexic, and muscle tone was similar to that of the awake cats (i.e., relaxed, not weight or load bearing, with minimal resistance to passive stretch). We monitored the kinematic effects of microstimulation and changes in electromyographic (EMG) activity in forelimb muscles. There was an age-dependent reduction in the number of sites where microstimulation did not produce a motor effect (i.e., ineffective sites), from 95% in animals younger than 60 days to 33% between 81 and 90 days. In adults, 24% of sites were ineffective. Median current thresholds for evoking movements dropped from 79 μA in animals younger than day 60 to 38 and 28 μA in day 81–90 animals and adults, respectively. There was a proximal-to-distal development of the somatotopic organization of the motor map. Stimulation at the majority of sites in animals younger than day 71 produced shoulder and elbow movement. Wrist sites were first present by day 71, and digit sites by day 81. Sites at which multiple responses were evoked, between 1.0 and 1.5 times threshold, were present after day 71, and increased with age. A higher percentage of distal joints were co-represented with other joints, rather than being represented alone. We found that effective sites initially were scattered and new sites representing proximal and distal joints filled in the gaps between effective sites. During most of the period examined, development of the caudal M1 subregion lagged that of the rostral subregion (percent of effective sites; threshold currents), although these differences were minimal or absent in adults. Our results show that the M1 motor representation is absent at day 45 and, during the subsequent month, the motor map is constructed by progressively representing more distal forelimb joints.

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