Electromyographic responses evoked in muscles of the forelimb by intracortical stimulation in the cat

Chronically implanted microwires were used to deliver brief trains of electrical stimuli (11 cathodal pulses at 330 Hz and intensity 5-35 microA) to sixty-two locations in the grey matter of the pericruciate cortex in cats. Electromyographic (e.m.g.) responses in the contralateral forelimb were recorded from a total of ten muscles (four to eight in each animal) acting about the shoulder, elbow and wrist and on the digits. The animals were relaxed with little background e.m.g. in the muscles and as a result only excitatory effects could be described. Five muscles which are flexors in the locomotor context were excited from more electrodes, distributed more widely across the motor cortex, than another five muscles which are extensors during locomotion; this difference in 'accessibility' was present both at 35 microA stimulus intensity and at 15 microA. At a stimulus intensity of 15 microA, effective cortical electrodes tended to cluster either in the most lateral part of the anterior sigmoid gyrus (rostromedial focus) or in the coronal gyrus just caudal to a line prolonged beyond the lateral end of the cruciate sulcus (caudolateral focus). This is consistent with the existence of a double motor representation within the forelimb motor cortex (Pappas & Strick, 1981). The two foci were similar in that both gave rise to more flexor than extensor responses and to fewer responses in digit or wrist muscles than in muscles acting about more proximal joints (elbow and shoulder). At stimulus intensity 35 microA the latency of the earliest e.m.g. responses ranged from 11 to 14 ms in different muscles. For some muscles and electrodes the amplitude of the e.m.g. responses was substantially altered by a quite small postural change. After pyramidectomy the cortical thresholds and the e.m.g. latencies were both greatly increased.

Forelimb electromyographic responses to motor cortex stimulation during locomotion in the cat

The forelimb motor cortex was stimulated via chronically implanted microelectrodes whilst electromyographic (e.m.g.) responses were recorded from muscles in the contralateral forelimb in cats walking steadily at 0.5 m/s. The stimuli were brief trains of 0.2 ms pulses (11 pulses at 330 Hz), intensity 5-20 microA and e.m.g.s were recorded from the following muscles: biceps brachii, brachialis, long and lateral heads of triceps brachii, latissimus dorsi, cleidobrachialis, extensor digitorum communis, palmaris longus and flexor and extensor carpi ulnaris. During locomotion, stimulation at 20 microA readily elicited brief, short-latency changes in the normal locomotor patterns of activity in all muscles studied. The changes included production of e.m.g. at times in the step cycle when the muscles are normally inactive and brief augmentations or diminution of the normal locomotor e.m.g.s. Individual electrodes usually influenced several muscles, and muscles acting antagonistically about the same joint were sometimes co-contracted. The first effect on locomotor flexor muscles (i.e. muscles active in relation to the swing phase of the step cycle) was almost always excitatory and such effects were often phase-dependent, usually occurring when the muscle was normally active or about to become active. Extensor muscles were excited from some cortical loci but inhibited from others (inhibitions were necessarily detectable only when the muscles exhibited locomotor-related e.m.g.s). Some micro-electrodes elicited excitation during swing (when the extensors are inactive) but elicited inhibition during stance. In several muscles the latencies of the excitatory e.m.g. changes could be as short as 6 ms measured from the first pulse in the stimulus train. In flexors, but not in extensors, latencies fluctuated according to the timing of the stimuli relative to the step cycle. Reduction in stimulus intensity reduced the amplitude of the e.m.g. changes, the number of muscles influenced and often increased the latency. However, both excitations and inhibitions were sometimes evident at 5 microA and thresholds for excitatory responses were, over-all, substantially lower than in the resting animal. Longer trains of stimuli were capable of resetting the step cycle. Response thresholds were greatly increased after pyramidectomy. These findings support the view that the natural bursts of impulses discharged by pyramidal tract neurones during steady locomotion are likely to contribute to regulating forelimb muscle activity on a step-by-step basis.

Forelimb responses to cutaneous nerve stimulation during locomotion in intact cats

The reflex responses of forelimb muscles to electrical stimulation of the cutaneous superficial radial nerve were recorded during treadmill locomotion in chronically implanted cats. In brachialis and cleidobrachialis (muscles which are active mainly during the swing phase) the responses were maximal during the swing phase and minimal or absent during the stance phase. In the long head of triceps which is active mainly during the stance phase, responses were also minimal during stance and maximal during swing. It is concluded that, for some muscles, the period of maximal reflex responsiveness can be out of phase with the period of the step cycle during which they are normally active.

Phase-dependent responses evoked in limb muscles by stimulation of medullary reticular formation during locomotion in thalamic cats

Electromyographic and kinematic responses of all four limbs were studied when loci within the medullary reticular formation (MRF) were stimulated (30-ms train of 0.2-ms pulses at 300 Hz, strength 35 microA) during treadmill locomotion in spontaneously walking thalamic cats. Responses could be evoked in flexor or extensor muscles of any given limb by such stimulation, depending on the time during the step cycle at which the stimulus was delivered. Stimulation normally excited flexor muscles but could either excite or inhibit extensor muscles depending on the exact position of the electrode. Excitatory responses in extensor muscles were often followed by a short period of inhibition of activity. The responses in muscles of the opposing limbs of the same girdle were, in general, reciprocally organized. For instance, a stimulus delivered during the swing phase of the ipsilateral limb normally evoked excitatory responses both in flexor muscles of that limb and in extensor muscles of the contralateral limb. The same stimulus delivered during the stance phase of the ipsilateral limb evoked excitatory responses in ipsilateral extensor muscles and in contralateral flexor muscles. Responses were also observed at the same time in fore- and hindlimbs that were well organized with respect to the locomotor cycle. Seventy-five percent of all responses occurred within 8-20 ms of the onset of the stimulus train. Responses evoked in muscles of the opposing limbs of one girdle (e.g., a flexor of one limb and an extensor of the other) had similar latencies, suggesting that the responses were synchronously organized on both sides of the body rather than one being a consequence of the other. Although the majority of responses in a given muscle were elicited during its period of activity, responses could occasionally be evoked when there was no activity in that muscle or could be absent despite activity in the muscle. The short trains of stimuli were normally potent enough to affect the limb trajectory, which reflected changes in the onset or the offset of the activity of most muscles. Thus the stimuli effectively changed both the duration of the period of activity in these muscles and the overall step cycle. Longer trains of stimuli (200 ms) markedly amplified these changes to the point of completely resetting the locomotor rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)

Topographical localization in the motor cortex of the cat for somatic afferent responses and evoked movements

Microwires chronically implanted in the pericruciate cortex of free-to-move cats were used to record extracellularly from cortical neurones and to deliver intracortical stimulation. Natural stimulation of cutaneous and/or deep mechanoreceptors in limbs and trunk evoked discharges in 89% of 165 neurones, 57% of which were pyramidal tract neurones. Out of 112 cells with receptive fields on the contralateral forelimb, 41% had cutaneous fields, 29% had fields involving deep tissues and 30% were driven from both sources. Cutaneous receptive fields were much commoner than deep ones among cells with fields including the forefoot; this relationship was reversed for cells with more proximal fields. Many more cells had distal than proximal fields. The 'zones' of the forelimb (i.e. foot, wrist, elbow, shoulder) provided input to widespread and overlapping cell populations within the coronal gyrus and the lateral parts of the anterior and posterior sigmoid gyri. Despite the overlap a somatotopy existed with successively more distal limb zones represented successively further laterally in the pericruciate area. Intracortical stimulation (eleven cathodal pulses, duration 0.2 ms, frequency 330 Hz, intensity 35 microA or less) evoked flick movements of the contralateral limbs which were abolished by pyramidectomy. In the forelimb, shoulder movements were commonest and elbow, wrist and digits were represented with decreasing frequency. Both for 35 microA and for threshold stimulation the distributions of the effective electrodes revealed an overlapping somatotopy such that the wrist movements were almost restricted to the coronal gyrus and shoulder movements were most often evoked from the lateral part of the anterior sigmoid gyrus. The movement and receptive field somatotopies overlapped heavily but the former showed a distinct lateral shift relative to the latter. As a result shoulder movements were not uncommonly evoked from the coronal gyrus although the shoulder provided almost no input to cells in that area.

Discharges of pyramidal tract and other motor cortical neurones during locomotion in the cat

A method is described for chronically implanting fine flexible microwires into cat motor cortex, which permitted extracellular recordings to be made from 165 single neurones. Most units were recordable for 12 h and some for up to 2 days. Of the neurones tested, 57% were shown to project to the medullary pyramid (pyramidal tract neurones, p.t.n.s). Antidromic latencies corresponded to a range of conduction velocities from 63 to 9 m/s. In the animal at rest neurones discharged at rates from 0.5 to 44 impulses/s. During locomotion at 0.5 m/s (a slow walk) 56% of cells discharged faster than at rest and 80% showed frequency modulations time-locked to the step cycle. Most fired one discrete burst of impulses per step or one peak period superimposed on a maintained discharge. In different cells peak activity occurred at widely different times during the step cycle. A few cells peaked twice per step. Peak rates (averaged over twenty steps) ranged from 10 to over 120 impulses/s, the values for most slow-axon p.t.n.s (conduction velocity less than 21 m/s) being lower than for any of the fast-axon p.t.n.s. For locomotion at speeds between 0.37 and 1.43 m/s a roughly linear relationship existed between discharge rate and speed in 14% of cells. However, the changes were modest and in most cells both mean rate and peak rate were unrelated to speed. In some cells discharge phasing was fixed (relative to the step cycle in the contralateral forelimb); in others there were progressive phase shifts (or more complex changes) as speed increased. During locomotion up a 10 degrees incline discharge phasings were the same as on the flat in all of the twenty-seven neurones studied and most showed no substantial change in mean rate or peak rate (although there were substantial increases in limb muscle electromyogram amplitudes).

Locomotor-related neuronal discharges in cat motor cortex compared with peripheral receptive fields and evoked movements

Discharge patterns of motor cortical neurones in cats walking steadily on a moving belt have been compared with other functional characteristics of the neurones. In forelimb motor cortex rhythmic discharges occurred in cells with peripheral receptive fields in all parts of the contralateral forelimb and also in cells with no discernible receptive field. Cells discharging at similar times during the step cycle often had very different receptive fields and cells with similar receptive fields (including neighbouring cells) could discharge at similar or at quite different times. In cells with a cutaneous receptive field including the forefoot the discharges during locomotion remained rhythmic (and their phasing relative to the step cycle was unchanged) when the response to mechanical stimulation in the receptive field was temporarily much reduced or abolished by local anaesthesia of the skin. The proportion of neurones showing accelerated firing during different parts of the step cycle fluctuated more for antidromically identified pyramidal tract neurones (p.t.n.s) than for non-p.t.n.s and was highest during the second half of stance in the contralateral forelimb and lowest during swing. When the neurones were subdivided according to the movement evoked by threshold electrical stimulation through the micro-electrode, p.t.n.s and non-p.t.n.s recorded by electrodes evoking elbow flexion showed a wide variety of discharge patterns. For p.t.n.s the discharge rate reached an average of 69 impulses/s during late stance and declined to an average of 26 impulses/s during swing.

A study of jaw reflexes of the awake cat during mastication and locomotion

This paper reports on experiments on the jaw opening reflex carried out while awake unrestrained cats were eating or walking on a treadmill. It is shown that the jaw opening reflex response to low intensity stimulation diminished in all phases of the masticatory cycle. The response to higher threshold afferents, however, is phase modulated so that the largest responses occur during the jaw closing phase. This is in accord with the need for increased protection of the soft tissues in this phase of the movement. In contrast, the digastric reflex amplitude does not change when the cat passes from quiet standing to walking on the treadmill. Evidence is presented that the electromyographic activity of the jaw closing muscles increases during upwards movement of the head during walking and decreases as the head falls. These data support the hypothesis that the myotatic reflex in the elevator muscles plays a role in stabilizing the mandible during locomotion.

A new lack of twist for the Judkins left coronary catheter

We have developed a modified Judkins left coronary arteriography catheter. The catheter is fabricated from 7 French thin-walled tubing made of extruded polyethylene. This tubing has a larger lumen diameter than either the 7 French or 8 French torque-control tubings used for standard Judkins coronary arteriography catheters. The large lumen substantially improves the pressure-flow characteristics of the catheter. Accordingly, it is considerably easier to inject contrast medium through this tubing. Although this tubing has no torsional rigidity, the lack of torque-control has proved to be an advantage rather than a detriment in the use of the catheter. Based on experience of over 2,000 studies with this catheter, we feel that it is superior to standard torque-control catheters for left coronary angiograms.

Responses in the posterior lobe of the rat cerebellum to electrical stimulation of cutaneous afferents to the snout

1. Responses in the cortex of the posterior lobe of the cerebellum to electrical stimulation of afferent fibres from the skin of the snout have been analysed in decerebrate and pentobarbitone-anaesthetized rats by means of surface and microelectrode records. Single shocks were applied either to the exposed follicles of the mystachial vibrissae or to the infraorbital branch of the trigeminal nerve. 2. In decerebrate rats responses were mediated only via mossy fibre afferents. Stimulation of one side of the snout yielded responses with mean latency 2.4 ms throughout the uvula (largest ipsilaterally and in lobule IXa). Smaller responses with similar latency were present in both cerebellar hemispheres (largest ipsilaterally). The earliest discharges of Purkinje cells in lobule IXa occurred at latencies between 4.5 and 8.5 ms. 3. All components of the extracellular field potentials generated within the cortex by the mossy fibre input were detectable by surface recording with ball electrodes. 4. The earliest surface potentials had a latency of 0.55 ms (peak latency 0.8 ms); they arose through volume conduction from the brain stem of a potential which signalled arrival of the primary afferent volley. The short delay between this event and the arrival of the mossy fibre volley in the cerebellum suggests that only one synaptic relay occurs in the brain stem. 5. In pentobarbitone-anaesthetized rats surface responses mediated via mossy fibres persisted and were accompanied at slightly higher threshold by responses shown to be mediated via climbing fibres. The latter were present in descending order of amplitude in three sagittally directed zones, one in contralateral Crus 2 (minimum latency 13 ms), one in the vermis contralaterally near the mid line in lobule IXa (latency 16 ms) and a third in ipsilateral Crus 2 (latency 20 ms) 6. In the hemisphere the responses mediated via climbing fibres occurred within the somewhat larger zones activated via mossy fibres but in the vermis the two types of trigemino-cerebellar input influenced quite separate areas of cortex.