Showing papers by "Mark Hallett published in 1993"
TL;DR: The normal influence of the basal ganglia on the prefrontal cortex may be required for timely access of information to and from the working memory buffer, while the cerebellum may index and order events in the time domain and be therefore essential for any cognitive functions involving sequences.
Abstract: We compared procedural learning, translation of procedural knowledge into declarative knowledge, and use of declarative knowledge in age-matched normal volunteers (n = 30), patients with Parkinson's disease (n = 20), and patients with cerebellar degeneration (n = 15) by using a serial reaction time task. Patients with Parkinson's disease achieved procedural knowledge and used declarative knowledge of the task to improve performance, but they required a larger number of repetitions of the task to translate procedural knowledge into declarative knowledge. Patients with cerebellar degeneration did not show performance improvement due to procedural learning, failed to achieve declarative knowledge, and showed limited use of declarative knowledge of the task to improve their performance. Both basal ganglia and cerebellum are involved in procedural learning, but their roles are different. The normal influence of the basal ganglia on the prefrontal cortex may be required for timely access of information to and from the working memory buffer, while the cerebellum may index and order events in the time domain and be therefore essential for any cognitive functions involving sequences.
476 citations
TL;DR: The electromyographic activity in several contralateral muscles showed that trains of rTMS applied to the motor cortex induced a spread of cortical excitability, which probably constituted an early epileptogenic effect ofrTMS.
418 citations
TL;DR: The results suggest that the cortical representation of the reading finger in proficient braille readers is enlarged at the expense of the representation of other fingers.
Abstract: We used focal transcranial magnetic stimulation to map the motor cortical areas targeting the first dorsal interosseous and the abductor digiti minimi muscles bilaterally in 10 proficient braille readers and 10 blind controls who were matched for age (mean, 50.6 yr) and age at time of blindness (mean, 7.5 yr). The proficient braille readers had learned braille at age 8 to 14 years and used it daily for 5 to 10 hours. Controls had not learned braille until age 17 to 21 years and used it daily for < 1 hour. In the controls, motor representations of the right and left first dorsal interosseous and abductor digiti minimi muscles were not significantly different. However, in the proficient braille readers, the representation of the first dorsal interosseous muscle in the reading hand was significantly larger than that in the nonreading hand or in either hand of the controls. Conversely, the representation of the abductor digiti minimi muscle in the reading hand was significantly smaller than that in the nonreading hand or in either hand of the controls. These differences were not due to differences in motor thresholds. Our results suggest that the cortical representation of the reading finger in proficient braille readers is enlarged at the expense of the representation of other fingers.
300 citations
TL;DR: The findings suggest that the temporary removal by ischaemic nerve block of myelinated afferent inputs reduces inhibition at the motor cortical level and that this disinhibition is responsible for the increased excitability of the corticospinal system.
Abstract: The amplitudes of motor evoked potentials to transcranial magnetic stimulation from muscles immediately proximal to a temporarily anaesthetized [Bier's block] human forearm increase in minutes after the onset of anaesthesia and return to control values after the anaesthesia subsides. In order to determine the level at which the early modulation of human motor outputs takes place, we recorded maximal H reflexes, peripheral M responses, motor evoked potentials to transcranial magnetic stimulation, and motor evoked potentials to transcranial electrical stimulation and spinal electrical stimulation from a muscle immediately proximal to a limb segment made ischaemic by a pneumatic tourniquest. The amplitudes of motor evoked potentials to transcranial magnetic stimulation, but not to transcranial electrical stimulation and spinal electrical stimulation, were larger during ischaemia, implying that the site of change was in the motor cortex. The maximal H/M ratios were unaffected by ischaemia, indicating that α-motor neuron excitability to segmental la inputs remained unchanged. The map of cortical representation areas for this muscle obtained with transcranial magnetic stimulation was also enlarged. Taken together, our findings suggest that the temporary removal by ischaemic nerve block of myelinated afferent inputs reduces inhibition at the motor cortical level and that this disinhibition is responsible for the increased excitability of the cortico-spinal system.
296 citations
TL;DR: The present study suggests that memory in patients with relatively pure cerebellar dysfunction is only partially compromised and that the impairment is secondary to a deficit in executive functions.
Abstract: Eleven patients with relatively selective cerebellar degeneration and 11 normal control subjects underwent a comprehensive neurologic and neuropsychological examination. The neuropsychological tests assessed general intellectual ability, different aspects of memory (effortful, automatic, and implicit memory processes), speed of information processing, and verbal fluency (using both category and letter fluency tasks). The results indicated that cerebellar patients were significantly impaired only on tasks requiring the use of executive functions, such as the initiation/perseveration subtest of the Mattis Dementia Rating Scale or the fluency tests, and on memory measures requiring greater processing effort. They performed normally on automatic and implicit measures of memory. Performance on the effortful memory and executive measures was not associated with neurologic variables or mood state. After controlling for the initiation/perseveration deficit, the effortful memory scores of the cerebellar patients were no longer different from those of controls. The present study suggests that memory in patients with relatively pure cerebellar dysfunction is only partially compromised and that the impairment is secondary to a deficit in executive functions.
285 citations
TL;DR: The role of the cerebellum and its associated brainstem circuitry in the acquisition of the conditioned response has been investigated in this paper, where the eye-blink conditioned response in five patients with pure cerebellar cortical atrophy and seven patients with olivopontocerebellar atrophy.
Abstract: There is evidence from animal experiments that the cerebellum and its associated brainstem circuitry are involved in the acquisition of the conditioned response. In order to obtain evidence for their involvement in humans, we studied classical delay conditioning, using the eye-blink conditioned response, in five patients with pure cerebellar cortical atrophy and seven patients with olivopontocerebellar atrophy. The results were compared with those obtained in a group of neurologically healthy volunteers matched with the patients for age and sex. The two groups of patients had similar abnormalities in the acquisition of the conditioned response and produced fewer conditioned responses than in the control subjects in any given block of trials. Many of the patients' conditioned responses were inappropriately timed with respect to the conditioned stimulus. These results support the role of the cerebellum in the expression and timing of the conditioned response.
247 citations
TL;DR: In six normal volunteers, including four of the investigators, the amplitudes of motor evoked potentials elicited by transcranial magnetic stimulation were transiently decreased after exercise, indicating fatigue of motor pathways in the central nervous system.
Abstract: Fatigue of voluntary muscular effort is a complex and multifaceted phenomenon. Fatigue of peripheral nervous system components, including the contractile apparatus and the neuromuscular junction, has been well studied. Central nervous system components also fatigue, but studies have lagged for want of objective methods. Transcranial magnetic stimulation is a relatively new technique that can be used to assess central nervous system excitability from the motor cortex to the alpha-motoneuron. In six normal volunteers, including four of the investigators, the amplitudes of motor evoked potentials elicited by transcranial magnetic stimulation were transiently decreased after exercise, indicating fatigue of motor pathways in the central nervous system. The decrease in amplitude was associated with a feeling of fatigue. The mechanism of this phenomenon is apparently decreased efficiency in the generation of the motor command in the motor cortex.
245 citations
TL;DR: The model proposes that the purpose of the basal ganglia circuits is to select and inhibit specific motor synergies to carry out a desired action.
Abstract: The pathophysiology of the movement disorders arising from basal ganglia disorders has been uncertain, in part because of a lack of a good theory of how the basal ganglia contribute to normal voluntary movement. An hypothesis for basal ganglia function is proposed here based on recent advances in anatomy and physiology. Briefly, the model proposes that the purpose of the basal ganglia circuits is to select and inhibit specific motor synergies to carry out a desired action. The direct pathway is to select and the indirect pathway is to inhibit these synergies. The clinical and physiological features of Parkinson's disease, L-DOPA dyskinesias. Huntington's disease, dystonia and tic are reviewed. An explanation of these features is put forward based upon the model.
215 citations
TL;DR: The normal velocity of gait and the normal step length argue against a parkinsonian-type disturbance, whereas the clinical picture suggests a disturbance of the cerebellum.
Abstract: Objective: To assess gait in patients with autism. Design: Clinical and physiologic assessment. Setting: Research hospital Patients and Subjects: Five adults with autism and five healthy, age-matched control subjects. Main Outcome Measure(s): Clinical and biomechanical assessment. Results: Clinical assessment showed mild clumsiness in four patients and upper limb posturing during gait in three patients. The velocity of gait, step length, cadence, step width, stance time, and vertical ground reaction forces were normal in all patients. The only significant abnormality was decreased range of motion of the ankle. Some patients exhibited slightly decreased knee flexion in early stance. Clinically, the gait appeared to be irregular in three patients, but the variability was not significantly increased. Conclusions: The findings in patients with autism indicate a nonspecific, neurological disturbance involving the motor system. The normal velocity of gait and the normal step length argue against a parkinsonian-type disturbance, whereas the clinical picture suggests a disturbance of the cerebellum.
192 citations
TL;DR: This study lends support to earlier suggestions that circuits involving the inferior olivary nuclei in the medulla and the thalmus are involved in the generation of essential tremor.
147 citations
TL;DR: The motor representation of APB, as defined by TMS, is not homogeneous but rather contains at least two components that differ physiologically and topographically.
Journal Article•
TL;DR: Ten patients, three with postural tremor and seven with action myoclonus, had stereotyped involuntary rhythmic movements when attempting to execute a sustained isometric muscle contraction, implying a greater dependence of this rhythmic phenomenon on a central generator than on peripheral feedback loops.
Abstract: Ten patients, three with postural tremor and seven with action myoclonus, had stereotyped involuntary rhythmic movements when attempting to execute a sustained isometric muscle contraction. The movements were characterized by rhythmic EMG bursts lasting less than 50 msec and appearing synchronously in agonist and antagonist muscles at a rate of 9 to 18 Hz. Backaveraging of the EEG activity related to the onset of the rhythmic EMG bursts identified a cortical potential preceding the EMG bursts in all patients. These symptoms and signs fit the description of "cortical tremor," a variant of cortical reflex myoclonus. Cortical tremor is common in patients with cortical myoclonus and may be a source of functional disability. In two patients in whom we studied the effects of graded levels of isometric force, force recruitment modulated the abnormal EMG bursting frequency, amplitude, and spatial distribution of the myoclonic jerks in the activated limb. Transcranial magnetic and electrical stimulation, but not peripheral nerve stimulation, influenced the abnormal EMG bursting pattern, implying a greater dependence of this rhythmic phenomenon on a central generator than on peripheral feedback loops.
TL;DR: This is the first study to offer evidence that patients with primary insomnia have objectively definable features during wakefulness that clearly distinguish them from normal subjects.
Abstract: Objective: In the absence of clear distinctions in alertness between patients with primary insomnia and normal subjects, the goal of this study was to identify psychometric and electrophysiological measures that would distinguish these two groups. Method: The daytime alertness of 20 primary insomnia patients and 20 normal subjects was investigated through their scores on a 26-item hyperarousal scale and measurement ofauditory evoked potentials and alpha and nonalpha band EEG activity. Statisticalanalysis ofthe data included correlation of the hyperarousal scores and the electrophysiological measures. Results: The hyperarousal scores showed clearly higher daytime alertness in the insomnia patients compared with the normal subjects. In addition, during wakefulness, the insomnia patients showed greater amplitudes ofP1N1, a durable, intrinsic, late (cortical) component ofthe auditory evoked potential, as well as greater EEG activity across the frequency spectrum. The hyperarousal scores correlated positively with the amplitude of P1N1 at each of three sound intensities. Conclusigns: To the authors’ knowledge, this is the first study to offer evidence that patients with primary insomnia have objectively definable features during wakefulness that clearly distinguish them from normal subjects. The measurement of hyperarousal might be used to refine descriptions of insomnia populations in experimental studies. (Am J Psychiatry 1993; 150:1529-1534)
TL;DR: The NINDS Myotatic Reflex Scale is devised and is now accepted by the NIH’s Clinical Center as an intramural research standard and is urged to be used elsewhere.
Abstract: In the Clinical Neuroscience Program, Division of Intramural Research, National Institute of Neurological Disorders and Stroke (NINDS), we have been concerned about the lack of a standard scale for the assessment of myotatic reflexes (tendon jerks, deep tendon reflexes, phasic muscle stretch reflexes). Fellows come to work here from all over the United States and the world. Communication about reflexes is difficult betweell physicians, and notes in the hospital chart are impossible to interpret. Taking note of the largely successful and nearly universal acceptance of the MRC rating scale for muscle strength’ and the common use of the Ashworth Scale for increased muscle tone,’ we devised the NINDS Myotatic Reflex Scale. As this scale is similar or identical to many scales already in u ~ e , ~ ~ we do not claim originality. Indeed, we chose the scale because of its similarity to these other scales. We have adopted the scale for use in the NINDS, and the other institutes a t the NIH have also agreed to use it. Thus, i t is now accepted a t the NIH’s Clinical Center as an intramural research standard. We urge its use elsewhere. The scale follows: 0 = reflex absent. 1 = reflex small, less than normal; includes a trace response
TL;DR: A feature of cerebellar ataxia is dysmetria, which is characterized by inaccurate movements, and studies of multijoint movements show abnormalities in relative timing of the different joints, suggesting that the prolongation of the neural signal is responsible for the kinematic abnormality.
Abstract: A feature of cerebellar ataxia is dysmetria, which is characterized by inaccurate movements Studies of rapid movements at a single joint show prolonged acceleration phases and prolonged initial bursts of EMG activity in the agonist muscle These two features correlate with each other, suggesting that the prolongation of the neural signal is responsible for the kinematic abnormality This explains a tendency to hypermetria Studies of multijoint movements show abnormalities in relative timing of the different joints During locomotion, knee and ankle motions can be delayed differentially with respect to the gait cycle Subjects attempting straight-line movements with the arm have systematic deviations that reflect incoordination of the shoulder and elbow with respect to each other A possible explanation of dysmetria is a failure of sufficient force generation within the necessary time to accomplish a coordinated movement Another possible explanation is that the cerebellum is responsible for timing of brain functions
TL;DR: The frequency content of signals encountered in clinical neurophysiology laboratories is described, guidelines for band-limiting frequencies are offered, and rules for determining minimal sampling frequencies are given.
TL;DR: The present study in normal subjects shows that the amount of inhibition increases with decreasing amplitude of the unconditioned H-reflex and with increasing intensity of the radial nerve stimulus.
01 Jan 1993
TL;DR: This chapter will emphasize the human work and information learned using the techniques of transcranial magnetic stimulation (TMS) (Cohen et al. 1991b), suggesting that the relationship between the motor cortex and its target muscles is modifiable, even in the adult brain.
Abstract: Although the role of each part of the brain in voluntary movement is incompletely known, it does appear that the main executor of voluntary movement is the primary motor cortex. Primary motor cortex has monosynaptic and oligosynaptic projections onto spinal motoneurons and a large percentage of cells that are active just prior to movement. Stimulation of these cells produces movement, and averaging of either cellular activity or regional brain potentials from this area shows a clear relationship to muscle activation. Until recently, the predominant view was that the anatomical and physiological relationship between the primary motor cortex and the spinal cord was immutable. Now there are a number of lines of evidence suggesting that the relationship between the motor cortex and its target muscles is modifiable, even in the adult brain. The evidence comes from both animal studies and human studies. This chapter will emphasize the human work and, specifically, information learned using the techniques of transcranial magnetic stimulation (TMS) (Cohen et al. 1991b). With TMS a pulsed magnetic field is applied over the scalp, and the resultant electric current flow in the underlying brain activates neurons. When the neurons activated are in the primary motor cortex, a muscle response or motor evoked potential (MEP) will be produced. By observing the MEPs and varying the stimulus intensity, it is possible to assess excitability of the motor system. Using a figure-8-shaped coil, the stimulus is rather focal, and by systematically moving the coil brain regions can be mapped. Some results will be reviewed using positron emission tomography (PET) with methods for measurement of blood flow. Activity of neurons induces an increase in regional cerebral blood flow, and this effect can be imaged.