Vision without proprioception modulates cortico-spinal excitability during hand motor imagery.

Several studies have shown a cortico-spinal facilitation during motor imagery. This facilitation effect is weaker when the actual hand posture is incompatible with the imagined movement. To determine whether the source of this interference effect arises from online proprioceptive information, we examined transcranial magnetic stimulation (TMS)-induced motor-evoked potentials during motor imagery in the deafferented subject G.L. The patient and 7 control subjects were asked to close their eyes and imagine joining the tips of the thumb and the little finger while maintaining a hand posture compatible or incompatible with the imagined movement. Contrary to control subjects' performance, G.L.'s results show that the facilitation observed during motor imagery was independent of the hand posture. To examine how vision of the hand interacts with the imagery process, G.L. and control subjects performed the same task with the eyes open. Like control subjects, when G.L. looked at her hand, a greater facilitation was observed when her hand posture was compatible with the imagined movement than when it was incompatible. These results suggest that in the absence of proprioception, vision may facilitate or inhibit motor representations and support the idea that limb position in the brain is organized around multisensory representations.

Localization without content. A tactile analogue of 'blind sight'.

We examined the ability of a patient, who had a cerebral lesion involving the left posterior hemisphere, to identify and to localize stimuli applied to her "deafferented" right upper limb. We observed a functional dissociation between localization and identification in both performance and subjective report. This finding may be a tactual analogue of "blind sight."

Mirror drawing in a deafferented patient and normal subjects: visuoproprioceptive conflict.

Results on a mirrow drawing task showed that a deafferented patient had no problem completing the pattern, whereas normal subjects needed more than four trials to attain a similar performance. The results suggest the presence of integrated visual and proprioceptive maps. The inversion of visual coordinates requires the need for a recalibration. Without proprioception, the task is more like a simple visual tracking task.

Gait of a deafferented subject without large myelinated sensory fibers below the neck.

We evaluated the gait pattern of a deafferented subject who suffered a permanent loss of large sensory myelinated fibers below the neck following an acute episode of purely sensory neuropathy 21 years ago. The subject has developed several strategies to achieve a secure gait, namely: (1) a reduction of the degrees of freedom by freezing the knee articulations during the stance phase, (2) a preservation of body balance by enlarging his base of support, and (3) visual monitoring of his step by stabilizing the head-trunk linkage together with a characteristic forward tilt. As a result, the gait of the deafferented subject lacks the fluidity of normal gait. Compared with normal subjects, the gait pattern of the deafferented subjects is characterized by a shorter cycle length, a longer cycle duration, a slower speed, and a lower cadence. Using a dual-task paradigm, the attentional demands for walking were particularly important (as indexed by longer probe reaction times) during the double-support phase, suggesting that the deafferented subject uses the double-support phase as a transitory stable phase to update cognitively the postural features necessary for generating his next step.

Role of afferent information in the timing of motor commands: a comparative study with a deafferented patient.

The accuracy of the motor system in synchronizing simultaneous movements initiations was tested in two conditions: (1) when the motor commands were triggered by an external signal (reactive condition), and (2) when subjects self-paced their movement onsets (self-paced condition). The task consisted of initiating simultaneously ipsilateral finger extension and heel raising. Eight normal subjects and a deafferented patient were tested. In the reactive condition, both normal subjects and the deafferented patient exhibited a precession of finger initiation over heel raising. This delay corresponds to the difference observed in the reaction time of the two limbs when measured independently. It reflects the difference in conduction times of the efferent pathways, as if the two motor commands were released simultaneously through a common triggering signal in the motor cortex. In contrast, in the self-paced condition normal subjects showed precession of heel over finger onsets, suggesting that synchrony is based upon the evaluation of afferent information. Unlike normal subjects, the patient showed no heel precession in the self-paced condition. These findings suggest that reactive and self-paced responses are produced through two different control modes and that afferent information contributes to the timing of motor commands in the self-paced mode.

Production of short timing responses: a comparative study with a deafferented patient.

How far can proprioception contribute to time keeping? To answer this question, a deafferented patient and neurologically normal subjects produced 1- or 5-sec durations in a sustained (continuous finger press) or discrete (two successive finger taps) manner, with and without Knowledge of Results. The findings were that: (1) proprioceptive afferents contribute to timing regulation in motor production of short durations; (2) this role can be rapidly compensated by Knowledge of Results; (3) the proprioceptive contribution is more important for sustained than for discrete performances; (4) stable performances are produced even when KR is withdrawn, suggesting familiarization with KR leads to the establishment of a mnemonic trace.

Tissue levels and displacement of in vivo labelled beta-adrenergic receptors by FM 24, an irreversible or slowly dissociable beta-blocker.

FM 24 [1-(2-exo-bicyclo[3,3,1]hept-2-ylphenoxy)-3-[(1-methylethyl)amino] 2-propanol hydrochloride] and propranolol were compared in mice with respect to their ability to displace in vivo 125I-hydroxybenzylpindolol which is selectively associated with beta-adrenergic receptor binding sites. After a simultaneous i.v. injection of the beta-blockers and 125I-hydroxybenzylpindolol propranolol was more active than FM 24. At an equiblocking dose i.e. a dose which inhibits by 80% the binding of 125I-hydroxybenzylpindolol, FM 24 was still effective after 6 h (40% inhibition in the brain and the heart, 60% in the lung) contrary to propranolol. After oral administration (2 mg/kg), 40% inhibition by FM 24 still persisted at 24 h in the heart whereas no effect of propranolol was detectable at 18 h. As the kinetics of [3H]FM 24 and [3H]propranolol after oral and i.v. administration are not very different we confirmed that the prolonged beta-blocking action of FM 24 was related to a tight irreversible binding to beta-receptors rather than to pharmacokinetic properties of this drug.

Evidence that clomethiazole interacts with the macromolecular GABA A-receptor complex in the central nervous system and in the anterior pituitary gland.

Clomethiazole (CLOM) is known to be an anticonvulsant drug and has been also reported to decrease serum prolactin (PRL) in humans. Both effects may be mediated by an enhancement of gabaergic transmission. In order to determine if (CLOM) interacts with GABA metabolism and/or at the GABA receptor level, we studied its effect on PRL release and on the binding of various compounds that interact with the GABAA-benzodiazepine-receptor complex. Intraperitoneal (IP) administration of CLOM to rats significantly decreased PRL levels, and this effect was antagonized by IP administration of bicuculline, an antagonist of the GABAA receptor. In vitro, the inhibitory effect of muscimol on PRL release from rat hemiadenohypophysis was potentiated in a dose-dependent manner by preincubation with CLOM. This effect was antagonized by picrotoxin (10(-6) M). On the other hand, CLOM had no effect on GABA metabolism and did not compete with GABAA, GABAB or benzodiazepine binding sites in cortical membranes. CLOM competed, however, with the picrotoxin binding site labelled with [35S]-butylbicyclophosphorothionate (TBPS), at an IC50 value of 1.2 x 10(-4) M, which is in the same range as some barbiturates. These results concerning PRL release and binding experiments with cortical membranes suggest that CLOM interacts with the picrotoxin/barbiturate site of the GABAA-receptor-chloride channel complex.

99Tcm-HMPAO-labelled leucocyte scintigraphy in suspected chronic osteomyelitis related to an orthopaedic device: clinical usefulness.

Thirty-five patients with suspected chronic osteomyelitis related to an orthopaedic device had 50 99Tcm-HMPAO-labelled leucocyte scans (LS). The scan appearances were compared with the bacteriological or clinical results and gave a sensitivity and specificity of HMPAO-LS of 83 and 100%, respectively. Bacteriological examination is often inaccurate in the diagnosis of osteomyelitis and therefore we assessed the clinical utility of HMPAO-LS. When the clinical, biological and radiological data were clearly suggestive of osteomyelitis (16/50) LS was unhelpful or even misleading when falsely negative (3/16). When the clinical, biological and radiological data were poorly suggestive of osteomyelitis (20/50) or conflicting (14/50) LS was misleading in only one patient (false negative). It is concluded that HMPAO-LS should only be performed to assist in the diagnosis of chronic osteomyelitis when there is no preexisting strong suspicion based on clinical, biological and radiological signs.

Visual motion cues in prismatic adaptation: evidence of two separate and additive processes.

The present study was based on the assumption that there are two visual channels which provide separate contributions to visuo-motor recalibration following prismatic displacement of the visual field. The functional properties of the two channels were assumed to conform to predictions from the two motion-analyzing systems models of visual motion perception. The results of the present study confirmed the predictions of the model. Whatever the type of illumination (continuous or stroboscopic) central vision utilizes only cues provided by visual exposure of the arm pointing to a stationary target. Peripheral vision utilizes only cues from visual exposure of the arm freely moving against the homogeneous background but this can be prevented by stroboscopic illumination. In peripheral vision, movement cues provided by exposure of a passively moved arm are not processed. In contrast, the processing of visual cues in central vision is unaffected by whether the movements are active or passive, provided that a stationary target is present. The effects of the two channels may be additive or competitive depending on the conditions. Experimental and theoretical implications are discussed.

The role of proprioceptive information for the production of isometric forces and for handwriting tasks.

A patient showing a total loss of all the large sensory myelinated fibers but intact peripheral motor system produced simple isometric force pulses and more complex tasks like handwriting and drawing. Overall, the patient was able to perform the isometric force task with an accuracy that approached that of normal subjects. The writing tasks, however, proved to be more challenging. In absence of vision, the different forms and cursive trajectories forming letters (morphocinetic components) were preserved but their localization within the constraints of the graphic space (topocinetic components) were severely impaired. These results demonstrate that, in absence of visual information, proprioceptive information is necessary to calibrate the hand in space.

[Motor neglect: issues and prospects]. / A propos de la négligence motrice: issues et perspectives.

Although the motor and sensory components of the neglect syndrome appear as dependent on a unitary attentional process, the clinical observation of pure motor neglect raises the possibility of segregation between attentional and intentional neural mechanisms. Neuroanatomical evidence suggests a separate role for the anterior and posterior cingulum. The anterior cingulum mainly projects to the supplementary motor area, the superior premotor area and the prefrontal granular cortex whereas the posterior cingulum mainly controls the inferior parietal lobule. The role of the intralaminar thalamic nuclei, together with the frontostriatal loops is considered. Behavioral neurology should strengthen its analytical approach in order to dissociate, by appropriate testing, the separate operations which contribute to relate perception and action. Several new hypotheses are presented.