Acceptability of Neuroscientific Interventions in Education.

Researchers are increasingly applying neuroscience technologies that probe or manipulate the brain to improve educational outcomes. However, their use remains fraught with ethical controversies. Here, we investigate the acceptability of neuroscience applications to educational practice in two groups of young adults: those studying bioscience who will be driving future basic neuroscience research and technology transfer, and those studying education who will be choosing among neuroscience-derived applications for their students. Respondents rated the acceptability of six scenarios describing neuroscience applications to education spanning multiple methodologies, from neuroimaging to neuroactive drugs to brain stimulation. They did so from two perspectives (student, teacher) and for three recipient populations (low-achieving, high-achieving students, students with learning disabilities). Overall, the biosciences students were more favorable to all neuroscience applications than the education students. Scenarios that measured brain activity (i.e., EEG or fMRI) to assess or predict intellectual abilities were deemed more acceptable than manipulations of mental activity by drug use or stimulation techniques, which may violate body integrity. Enhancement up to the norm for low-achieving students and especially students with learning disabilities was more favorably viewed than enhancement beyond the norm for high-achieving students. Finally, respondents rated neuroscientific applications to be less acceptable when adopting the perspective of a teacher than that of a student. Future studies should go beyond the acceptability ratings collected here to delineate the role that concepts of access, equity, authenticity, agency and personal choice play in guiding respondents' reasoning.

Motor unit synchronous firing as revealed by determinism of surface myoelectric signal.

Information on motor strategies can be extracted from the surface electromyogram (EMG) by non-linear methods. The percentage of determinism (%DET) obtained from recurrence quantification analysis (RQA) may be a sensitive variable to detect synchronous motor unit behaviour. The purpose of the present study was to validate this methodology by comparing it with an established technique estimating the degree of synchronization of pairs of voluntary activated motor units from the correlation of their firing in the time-domain. Single motor unit activity was recorded in extensor carpi radialis (ECR) muscle by pairs of tungsten microelectrodes inserted into the muscle belly. Cross-correlation analysis was performed in order to determine synchronization peak area by computing synchronous impulse probability. Surface EMG activity was recorded in parallel by electrodes placed over the skin of the same muscle and %DET was used as a measure of synchronous activity. The %DET appeared to be a valid measure of synchronization yielding results comparable to those obtained with cross-correlation analysis. Increases in %DET (t = 64.59, P < 0.0001) highly correlated (r2 = 0.70, P = 0.0013) with pharmacologically induced increases in the synchronization activity of pairs of ECR motor units (t = 8.71, P < 0.0001). RQA may be used as an alternative methodology for testing synchronous motor unit behaviour from surface EMG under physiological and pathological conditions.

Ia presynaptic inhibition in human wrist extensor muscles: effects of motor task and cutaneous afferent activity.

The task-dependence of the presynaptic inhibition of the muscle spindle primary afferents in human forearm muscles was studied, focusing in particular on the modulation associated with the co-contraction of antagonist muscles and the activation of cutaneous afferents. The changes known to affect the motoneuron proprioceptive assistance during antagonist muscle co-activation in human leg and arm muscles were compared. The evidence available so far that these changes might reflect changes in the presynaptic inhibition of the muscle spindle afferent is briefly reviewed. The possible reasons for changes in presynaptic inhibition during the antagonist muscle co-contraction are discussed. Some new experiments on the wrist extensor muscles are briefly described. The results showed that the changes in the Ia presynaptic inhibition occurring during the co-contraction of the wrist flexor and extensor muscles while the hand cutaneous receptors were being activated (the subject's hand was clenched around a manipulandum) could be mimicked by contracting the wrist extensor muscles alone while applying extraneous stimulation to the hand cutaneous receptors. It is concluded that besides the possible contribution of inputs generated by the co-contraction of antagonist muscles and by supraspinal pathways, cutaneous inputs may play a major role in modulating the proprioceptive assistance during manipulatory movements.

Participation of the red nucleus in motor initiation: unit recording and cooling in cats.

Cats were trained to release (Go) or not to release (No-go) a lever after a brief auditory signal, depending on the presence of an additional tone (No-go cue). Unit recording and cooling were made in the red nucleus (RN) contralateral to the performing limb. Three major results were found: (1) in the Go condition, we observed phasic increases of rubral firing, with a constant latency after the auditory signal and with an amplitude correlated to the latency of motor triggering (i.e. reaction time, RT); the tonic activity preceding the auditory signal could also be correlated to the RTs for some units; (2) in the No-go condition, there was no phasic increase of rubral firing after the auditory signal; the tonic activity during the presentation of the No-go cue was markedly decreased compared to the Go trials; (3) cooling of the RN increased the RTs and could also block the motor triggering. These results suggest that the RN is involved in setting and triggering a conditioned motor response according to sensory cues.

Changes in motor performance and rubral single unit activity in cats after microinjections of serotonin into the red nucleus area.

The serotonergic control exerted on the red nucleus (RN) was studied in unrestrained cats during the performance of a simple reaction time task which consisted of releasing a lever in response to an auditory go-signal. The effects of microinjections of serotonin-oxalate salt into the rubral area on the motor activity and on the firing of neurons recorded concomitantly in the red nucleus were investigated. Injections of serotonin (5-HT) (200-400 ng) into the red nucleus or its dorsal border induced subtle alterations in the conditioned motor performances but had no major effects on the spontaneous motor behavior. The changes in the conditioned motor output (an increase in the static force exerted on the lever and a speeding up of the lever release) are reminiscent of the facilitatory influence of serotonin on various motor reflexes previously reported. Changes in the neuronal activity were observed concomitantly with the effects on the motor output: 5-HT either enhanced or reduced the firing rate of the rubral neurons. These effects were apparently dependent on the discharge pattern of the neurons during the static motor activity. The results suggest that the serotonergic input to the red nucleus may participate in motor control by exerting a dual modulatory action on the activity of rubral neurons.

Electromechanical coupling and synchronous firing of single wrist extensor motor units in sporadic amyotrophic lateral sclerosis.

Electrical and contractile properties of motor units (MU) were studied in the extensor carpi radialis muscles during voluntary contraction. The discharge of 234 single MUs was recorded in 11 patients with sporadic amyotrophic lateral sclerosis (ALS) and compared with that of the 260 MUs recorded in 12 healthy control subjects. Characteristics of the MU twitches and of the macro-potentials, the electromechanical coupling and the synchronization of the motor neurone discharges, were compared. In 5 patients (population ALS1), the twitch contraction force and macro-MUP area values were much larger than those of the controls. In the 6 other patients (population ALS2), the twitch force was considerably depressed, whereas the macro-MUP area was slightly, but significantly, increased. In ALS1, as well as in ALS2, the electromechanical coupling was much weaker than in the controls, and the fast-contracting MUs were more severely affected than the slowly contracting MUs. The motoneuronal synchronization was assessed by performing cross-correlation analysis on MUs discharges, and was used as an index to the strength of the common motoneuronal inputs. The rate of occurrence of synchronous firing was conspicuously lower in both populations of patients than in the control group. This might reflect the loss of corticospinal projections that occurs in ALS. The data are discussed in terms of the time course of motor neurone axonal sprouting, and in terms of the neuronal and muscular dysfunction possibly involved in ALS disease.

Task dependence of Ia presynaptic inhibition in human wrist extensor muscles: a single motor unit study.

OBJECTIVE: Task-dependent changes in the Ia presynaptic inhibition generated by flexor group I afferents were investigated in 25 identified motor units (MUs) located in human extensor carpi radialis (ECR) muscles. METHODS: Seven subjects had to voluntarily contract their ECR muscles either alone during isometric wrist extension or concurrently with their wrist and finger flexor muscles while clenching their hand around a manipulandum. The MU reflex responses to the radial nerve stimulation (test stimulation) yielded narrow peaks in the post-stimulus time histograms (PSTH). The Ia presynaptic inhibition induced while stimulating the median nerve (conditioning stimulation) 20 and 40 ms before the radial nerve was assessed from the changes in the contents of the first 0.5 ms in the peaks. RESULTS: With both stimulation intervals, the Ia presynaptic inhibition, as assessed from the first 0.5 ms of the PSTH peaks, was consistently weaker during hand clenching. With both motor tasks, the Ia presynaptic inhibition was strongest at the 20 ms interval, in which it showed a downward gradient, working from slow to fast contracting MUs. With both intervals, the presynaptic inhibition was consistently weaker during hand clenching. The decrease in the Ia presynaptic inhibition observed at the 40 ms conditioning-test interval was less pronounced during wrist extension. CONCLUSION: It is suggested that the reason why Ia presynaptic inhibition was weaker during hand clenching may have been that this task involved numerous cutaneous inputs originating from the palm and finger tips. During gripping tasks, these cutaneous inputs may therefore contribute to adjusting the wrist stiffness by relieving the presynaptic inhibition.

Activity of caudate nucleus neurons in cat performing a reaction time task.

During a reaction time task, single units were recorded in the caudate nucleus of freely moving cats. Neuronal changes of activity were related to CS, to initiation of movement or to reinforcement. It is suggested that these changes of activity are involved in a process in which informations on the CS and on the on-going movement are associated with information on the occurrence of reinforcement.

Is the human masticatory system devoid of recurrent inhibition?

The aim of the present study was to investigate the existence or otherwise of a functional recurrent inhibitory system (Renshaw cell system) in the motoneurons that innervate human masticatory muscles. In a previous study, L: -acetylcarnitine (L: -Ac), a substance known to potentiate recurrent inhibition in humans was found to alter, in a specific way, the discharge variability, and the synchronous activity of motor units depending on the presence or absence of recurrent inhibition in the corresponding motoneuron pool. Using a similar paradigm, we have recorded the tonic discharge activity of motor unit pairs from the masseter muscle during voluntary isometric contraction while subjects were undergoing continuous intravenous saline (SAL, NaCl 0.9%) perfusion. Following a brief baseline-recording period, the subjects were given a test injection of either L: -Ac or isotonic saline (SAL) in a double blind manner. The variability, synchronization, and coherence between the motor unit discharges were analysed during three successive periods: pre-injection, during injection, and post-injection, each lasting 2-3 min. Neither L: -Ac nor SAL injection induced a significant change in the inter-spike interval (ISI) or the coefficient of variation of the ISIs in the motor units tested. There were also no significant changes in the pattern of synchronous activity or in the coherence, which reflects the common frequency content of the unit discharges. Reminiscent of what had been observed previously with motoneurons without recurrent inhibition in the Abductor Digitorum Minimi muscle, the lack of effects of L: -Ac injection on the firing behaviour of masseter motoneurons may suggest that classical Renshaw cell inhibition is lacking in this motoneuron pool.

Covariation of corticospinal efficiency and silent period in motoneuron diseases.

For a better understanding of the changes affecting the cortically induced silent period (SP) in motoneuron disease, the excitatory and inhibitory effects of transcranial magnetic stimulation were explored repeatedly in 8 patients with amyotrophic lateral sclerosis (ALS), 3 patients with Kennedy's disease (KD), and 10 healthy subjects. In KD, the background electromyogram (EMG) and the motor evoked potential (MEP) area were both enhanced. However, neither the corticospinal efficiency (MEP gain, the ratio between MEP and background EMG) nor the duration of the SP differed from healthy subjects. In ALS patients, the MEP gain and the SP duration decreased conspicuously with time. We conclude that use of the MEP gain improves detection of corticospinal dysfunction in ALS patients. Part of the SP shortening in ALS seems to reflect the reduced activation of cortical or spinal inhibitory networks by the abnormal corticospinal pathway.

Activity-related changes in electrical thresholds of pyramidal tract axons in the behaving monkey.

In monkeys generating torques about the wrist we investigated changes in the excitability of pyramidal tract (PT) axons, measured as the probability of evoked antidromic responses in motor cortex with constant juxtathreshold stimuli delivered in the brain stem. When PT stimuli were delivered 2-20 ms after an orthodromic action potential in the PT neuron, the excitability of axons was elevated, with a characteristic post-spike time course. Excitability peaked at a post-pike delay of 7.0 +/- 2.7 ms (n = 33). Axonal thresholds typically dropped to 80-90% of the unconditioned values (obtained for stimuli with no preceding spike). Controlling for such post-spike threshold changes by delivering stimuli at fixed post-spike delays, we found that excitability of many PT axons also fluctuated with the wrist responses, being slightly higher during flexion or extension. The place of movement in which excitability increased had no consistent relation to the phase of movement in which the PTN fired. Task-related threshold changes were also seen in PTNs whose discharge was not modulated with the wrist response. Delivering a subthreshold conditioning stimulus also increased the excitability of most PT axons to a subsequent test stimulus. Such post-stimulus changes may be mediated by the effects of adjacent fibers activated by the conditioning stimuli. The post-spike and post-stimulus changed added in a nonlinear way. All three types of threshold change may be mediated by a common mechanism: changes in the ionic environment of the axon produced by activity of the axon itself or its neighbors.(ABSTRACT TRUNCATED AT 250 WORDS)

Periodontal mechanoreceptor input reduces synchronous discharge of voluntarily activated masseter motor units in man.

The control exerted by inputs from periodontal mechanoreceptors (PMRs) on the tonic activity of 35 pairs of single motor units in the left masseter muscle was investigated with and without the presence of continuous pressure on the upper left central incisor tooth. Cross-correlograms were computed to assess the temporal coupling between the discharges of the motor unit pairs. In the absence of continuous pressure, central peaks in the cross-correlograms revealed the presence of significant synchronous discharge in 16 out of the 35 pairs tested. In contrast, during PMR stimulation only nine pairs were found to discharge with a significant amount of synchronization. It is concluded that short-term synchronization due to common, partially common and synchronized inputs shared by the motoneurons was reduced whenever extraneous periodontal inputs were superimposed on the voluntary command. This indicates that the interneurons which mediate the periodontal inputs arising from one single tooth are not distributed widely throughout the masseter motoneuron pool. In contrast, it appears that periodontal inputs are liable to reduce the efficiency of common inputs distributed to the masseter motoneurons during voluntary contraction ("desynchronization").

Firing pattern of type-identified wrist extensor motor units during wrist extension and hand clenching in humans.

1. Single motor unit activity was investigated in the extensor carpi radialis muscles during voluntary isometric contraction involving either the coactivation of the wrist agonist extensor muscles (wrist extension) or the coactivation of the wrist and finger antagonist extensor and flexor muscles (hand clenching). 2. The motor units were found to be activated at a similar level of motoneurone pool drive during both wrist extension and hand clenching, as indicated by the fact that the EMG activity at which they were recruited was practically the same in both cases (mean +/- S.D.: 20 +/- 26 and 21 +/- 25 mV, respectively). In addition, the net excitatory drive exerted on the motoneurones, as assessed from the mean interspike intervals, did not differ significantly between the two tasks (mean +/- S.D.: 104.57 +/- 17.24 and 103.01 +/- 16.26 ms, for wrist extension and hand clenching, respectively). 3. However, the discharge variability, in terms of the coefficient of variation of the interspike intervals, was slightly but significantly greater during hand clenching than during wrist extension (0.213 +/- 0.049 and 0.198 +/- 0.045, respectively). This increase involved all types of motor units, regardless of their contractile force. 4. We suggest that the greater motoneurone discharge variability observed during hand clenching may be attributable to an increase in the synaptic noise. This increase might be due to the activation of numerous afferent pathways mediating reciprocal interactions between antagonist motoneurone pools, as well as to the activation of hand cutaneous receptors that play a major role in the regulation of handling and gripping motor activities.

Activity of ventrolateral thalamic neurons in relation to a simple reaction time task in the cat.

Unrestrained cats performed ballistic forelimb flexion movements triggered by an auditory stimulus (CS) on a simple reaction time (RT) paradigm. During the variable foreperiod the subject was required to hold down a lever and to release it on presentation of the CS. The RTs ranged from 200 to 300 ms. The activity of single neurons of the ventrolateral nucleus of the thalamus (VL) was recorded bilaterally. More than 40% of the 166 units recorded in the VL contralateral to the performing limb presented, after the CS, changes of activity with a latency less than 100 ms and were classified into three types: (1) Twenty-five units had a short latency transient increase of activity 10 to 30 ms after the CS, followed by a longer increase or decrease in activity. Short latency increase as well as subsequent increase of the firing rate were not correlated to the RTs. (2) Twenty-nine units showed a 40-60 ms latency increase of activity which lasted long enough to continue during the forelimb movement. These units displayed a correlation between the RTs and the mean firing rate measured in the 40-100 ms period after the CS. The more the cells were activated, the shorter the RTs. (3) Fifteen units presented a reciprocal pattern of discharge with respect to the type (2) units. The firing rate decreased with latencies ranging from 20 to 90 ms after the CS. Only 14,5% of the 96 units recorded in the VL ipsilateral to the performing limb presented changes of activity starting in the 100 ms period following the CS. Background firing levels as well as phasic activity were rather low compared to those observed contralaterally. Sixteen units showed burst activity while the cat was performing but burst pattern was not time-related to the task. In an unconditioned animal, a very low level of activity and an absence of modulations were observed in both VLs.

Effects of ventrolateral thalamic nucleus cooling on initiation of forelimb ballistic flexion movements by conditioned cats.

Five cats were trained to perform a forelimb ballistic flexion on a reaction time paradigm including an upper limit of about 400 ms for reinforcement (food pellets). They were implanted with a cyrogenic probe thermically insulated, except at the tip, by a vacuum jacket (outer diameter, 1.1 mm). Four cats had the probe inserted into the ventrolateral thalamic nucleus (VL), contralateral to the moving limb. During cooling they showed increased reaction times, which remained constant throughout daily sessions performed during many weeks, independent of the foreperiod but varying from 25 to 100 ms according to the subject. The temperatures used to upset the reaction times varied from +10 decrees C to -8 degrees C, depending on the localisation of the probe and on the insulation of the silver tip used to prevent nervous tissue reaction, but for each subject the reaction times always increased when the temperature was lowered. The fifth cat, with a probe inserted between VL and the Centre Median, showed a decrease of reaction times on cooling to 0 degrees C and an increase of the reaction times for a cooling at -10 degrees C. For one of the four cats with a probe properly inserted into the VL, strain-gauges were stuck on the lever to measure the latency of the decrease of the pressure exerted by the subject when the subject initiated the forelimb flexion in response to the CS. Reaction times and latencies of pressure changes were closely correlated with the movement onset, and they were equally delayed during cooling. This result demonstrates that it is not by slowing down movement velocity that reaction times are upset during VL cooling but by delaying the movement onset.

Correlated changes in the firing rate of human motor units during voluntary contraction.

Spike trains of long duration were recorded from concurrently active pairs of motor units in the human masseter and tibialis anterior muscles. An innovative analysis technique was used to investigate functional coupling between the motoneurons by plotting the discharge frequency of one motor unit with respect to the firing times of the other (peri-spike frequencygram). Conventional cross-correlograms of discharge times were also constructed for each pair to detect synchronous firing and to compare them with the peri-spike frequencygrams (PSFs). The PSFs were examined with the hypothesis that, if the net common input of the two motoneurons was excitatory, the firing frequency of both units should increase around the time of the synchronous discharge of both units (i.e., time zero in the cross-correlogram). Conversely, if the net common input was inhibitory, the firing frequency of both units should fall around time zero. In 24 out of 37 masseter pairs tested, either one (n = 20) or both (n = 4) units of the pair displayed a statistically significant increase (P < 0.001) in the firing frequency around time zero of the PSF. No significant decrease in the discharge frequency was ever detected in any of the units of the 37 pairs tested. The probability of occurrence of a significant increase in firing rate was found to be significantly higher X2 = 5, P < 0.05) in the pairs with significant synchronous firing (13 out of 15) than in the pairs without (11 out of 22). Moreover, the percentage increase in the discharge frequency was found to be significantly higher in the pairs with significant synchronous activity (1.4%) than in those without (0.74%). In 24 out of 56 tibialis anterior pairs tested, either one (n = 19) or both (n = 5) units of the pairs displayed significant changes (P < 0.001) in discharge frequency around time zero of the PSF. A reduction in the mean firing rate starting about 20 ms before time zero and ending around time zero was most commonly detected in the PSF, the probability of this occurrence being significantly higher (X2 = 6.7, P < 0.01) in the pairs with significant synchronous discharges (18 out of 41) than in the pairs without (1 out of 15). However, the mean percentage fall in the firing frequency during this "inhibitory" phase did not correlate in amplitude with the presence or the absence of significant synchronous activity (-1.4% and -1.1% respectively). In many of the cases, this "inhibitory" period was followed by an "excitatory" period where the firing frequency displayed a significant increase (from about 6 ms to 20 ms past time zero). Such dual changes in the firing rate were only found in the pairs with significant synchronous activity (13 of the 41 pairs). The mean percentage increase in the firing frequency during the "excitatory" phase was significantly higher in the pairs with synchronous firing than in the pair without (1.4% and 0.5% respectively). The specificity of the frequency changes was assessed by performing control analyses where the discharge from one unit was cross-correlated with the discharge from the other unit at a different time (time-shuffled pairs). Synchronisation peaks were never observed in the cross-correlograms of the time-shuffled pairs. Furthermore, none of the 18 time-shuffled pairs in the masseter showed significant frequency changes in the same time period as that seen with the non-shuffled pairs. In the tibialis, only 1 out of 31 time-shuffled pairs showed a significant frequency change in one motor unit, and that was in the opposite direction to the frequency changes found in the non-shuffled pairs. It is suggested that the PSF analysis is an important tool for investigating the functional relationship between individual motoneurons as they fire voluntarily.

The "size principle" and synaptic effectiveness of muscle afferent projections to human extensor carpi radialis motoneurones during wrist extension.

The question of whether muscle spindle afferents might control human motoneurone activity on the basis of the "size principle" during voluntary contraction was investigated by recording the discharge of single motor units (n = 196) in wrist extensor muscles while stimulating the homonymous muscle spindles by means of tendon taps. The mechanical stimuli were delivered with a constant post-spike delay of 80 ms so that the resulting afferent volleys could be expected to reach the motoneurones towards the end of the inter-spike interval (mean +/- SD duration: 124.7 +/- 11.9 ms). In the six subjects tested, the response probability was found to be significantly correlated with the motor units' functional parameters. Differences in twitch rise times, twitch amplitudes, recruitment thresholds and macro-potential areas were found to account for 18%, 9%, 6% and 2% of the differences in the response probability observed within the whole population of motor units tested. These differences could not be due to differences in firing rate for two reasons: first, the motor units were found to discharge with a similar range of inter-spike intervals whatever their functional characteristics; secondly, the weak positive correlation observed between the response probability and the motor unit firing rate showed parallel regression lines between the late-recruited fast-contracting motor units and the first-recruited slowly contracting motor units, but the y-intercept was significantly higher in the latter case. This confirmed that the responses of the first-recruited slowly contracting motor units tended to be larger whatever the firing rates. In most of the pairs tested in the same experiment, the motor units which had the lowest recruitment thresholds, longest contraction times, smallest contraction forces or smallest motor unit macro-potentials tended to produce the largest responses, which also had the longest latencies. Taking the response latency to be an index of a motoneurone's conduction velocity and therefore of its size, the data obtained with this index and with other functional indices such as the twitch rise times and amplitudes, the macro-potential areas and the recruitment thresholds-can be said to be fully consistent with the "size principle", as previously found in anaesthetized animals. It can be inferred that the presynaptic inhibition which is liable to take action during voluntary contraction does not seem to alter the graded distribution of the muscle afferent projections to human wrist extensor motoneurones.

Scheduled-training of cats to a simple reaction time performance.

Cats were trained to release a lever at the onset of a sound, using a simple reaction time paradigm with different foreperiods. The training of the subjects was controlled by a PDP 8/L computer with a training schedule that avoided the problems of manual shaping except for the preliminary step, the lever press. This schedule successfully trained the cats in about 6 daily sessions up to the reaction time paradigm with a 3 sec criterion. In contrast, a programme designed to reduce the criterion value so as to induce the subjects to perform shorter latency movements failed because the cats learned to control it through an escape procedure.

GABAergic mechanisms in the cat red nucleus: effects of intracerebral microinjections of muscimol or bicuculline on a conditioned motor task.

Interneurons in the Red Nucleus (RN) are known to be under cortical control and to exert an inhibitory action, mediated by GABAergic mechanisms, on the main output towards the spinal cord. The effects of discrete injections of a GABA receptor agonist (muscimol) or an antagonist (bicuculline) in the Red Nucleus were tested on a motor task performed by seven cats. The subjects were trained to release a lever with a flexion movement of the forelimb controlled by a reaction time (RT) paradigm. Muscimol as well as bicuculline increased RTs in a dose-dependent manner at doses below 100 ng. However the parameters of the force exerted on the lever were differentially altered by the two drugs. Muscimol increased RTs by slowing down the force change preceding movement as well as slightly delaying its latency. While bicuculline increased drastically the force change latency. It could also speed up the force change velocity for low doses. At higher doses (up to 500 ng) both drugs produced an arrest of the performance either associated with anxiety signs (bicuculline) or dystonic movements of the head followed by body rotations (muscimol). The strong motor impairments as well as the disruption of the conditioned performances following muscimol or bicuculline microinjection in the RN suggest an important functional role for GABAergic interneurons. Under the control of cortical afferences they can modulate rubrospinal activity and participate in the triggering of a conditioned movement.