Biomedical subjects

J M Coquery

Publications and source records attributed to J M Coquery.

16 recordsLinked to original sources

PubMed1989

Specific modulation of the Hoffmann reflex cutaneous facilitation during a reaction-time task.

The Hoffmann (H) reflex and its facilitation produced by electrical stimulation of the sural area were examined before a ballistic extension of the right foot. Modulations of the cutaneous facilitation of the H reflex (CFH) were used to assess the control exerted over the transmission of low threshold cutaneous afferents. The time-course of H and CFH changes were investigated at the end of the foreperiod and during the premotor period, i.e. between the response signal and the onset of the electromyogram (EMG) of the soleus muscle. Four stimulation conditions were set up depending on whether the H reflex was elicited on the contracting or non-contracting limb, and whether cutaneous stimulation was ipsilateral or contralateral to the reflex. During the 100 ms preceding the response signal, the inhibition of the H reflex was more marked in the contracting limb than in the non-contracting limb. At the end of the foreperiod, the CFHs had a symmetric time course: the CFHs evoked by conditioning stimulation of the contracting limb were facilitated just before the response signal, while those produced by conditioning stimulation to the non-contracting limb were depressed. It is suggested that these variations are related to postural adjustments taking place before the movement is performed. As previously reported, the H reflex of the contracting limb exhibited a marked increase in amplitude over the 50 ms preceding the EMG. Reflex facilitations showed specific variations according to the ankle stimulated and the soleus muscle tested. The CFHs produced by stimulation of the non-contracting limb regained, at the end of the premotor period, a value close to their reference level recorded in trials without movement. The CFHs, produced by conditioning stimulation of the contracting limb were modulated differently according to whether the tested soleus muscle was contracting or not: when the CFH was tested on the contracting muscle, it was found to be depressed throughout the premotor period; this contrasted significantly with the isolated depression recorded on the non-contracting muscle. Therefore, only the cutaneous afferents from the mobilized limb, modulating the H reflex of the same limb, were subject to a specific inhibition during the premotor period. Throughout the preparatory and premotor periods, negative correlations were observed between H and CFH amplitude, except just before the EMG onset in the condition where the H reflex was delivered to the contracting muscle and the cutaneous stimulation to the ankle of the non-contracting limb: in this case, CFH amplitude increase paralleled that of the reflex amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1988

Orientation of attention and sensory gating: an evoked potential and reaction time study in cat.

Somesthetic-evoked potentials (SEPs) were recorded in eight cats trained to perform a reaction time task (RT). The preparatory period (PP) preceding the RT began with the cat placing its paw in a box and ended 1.5 s later with a paw-withdrawal signal, an imperative stimulus (IS). In experiment 1 (E1), the IS took the form of a vibration in the box, whereas in experiment 2 (E2) a tone was used. The SEPs were elicited by electrical stimulation delivered to the paw once per trial and at a different moment during the last second of each PP. The SEPs were recorded in the lemniscus medialis (LM), the centrum medianum (CM), and over the anterior suprasylvian gyrus (ASSG). During the PP of E1 (four cats), SEPs recorded in the CM and over the ASSG were found to be significantly depressed. No significant change was noted, however, in those recorded in the LM. No significant SEP depression was found in any of the structures in E2 (four cats). Comparison between the two experiments revealed notable differences at both the thalamic and cortical levels. Moreover, SEP depression diminished as the moment for the IS approached. While, in E1, this occurred in the CM and over the ASSG, in E2 it was found in the CM only. Lemniscal and thalamic SEP amplitude was found to be correlated with performance. These findings are discussed in terms of orientation of attention, discrimination, and sensory gating.

Animals↗

PubMed1985

[Modulation of cutaneous evoked potentials during the period preparatory to a reaction time task in the cat].

Evoked potentials (EP) were elicited in four cats either when they sat still or when they performed a reaction time (RT) task. The foreperiod (FP) of the RT situation started with the cat placing his paw on a platform and ended 1.5 sec later with the vibration of the platform, used as a signal to withdraw the paw. The paw was electrically stimulated, once per trial, during the last second of the FP. Evoked potentials were recorded in the medial lemniscus (ML), in the thalamic nucleus centrum medianum (CM), in the internal capsule (IC) and over the anterior suprasylvian gyrus (ASSG). On the average, the EPs recorded in the CM, in the IC and over the ASSG (early and late waves) were significantly reduced during the FP. The EPs recorded in the ML did not show any significant change. The reduction in the EPs amplitude decreases along the FP, being the less at the time of arrival of the response signal. Neither the amplitude nor the time course of the EPs are correlated with the RT duration. These results are discussed with reference to the concepts of preparation for movement and of anticipation of the response stimulus.

Afferent Pathways↗

PubMed1983

Effects of spatially oriented attention on the facilitation of the H reflex by a cutaneous stimulus.

The effects of spatially oriented attention on the facilitation of the H reflex induced by a mild electrical stimulation of the sural nerve was investigated in 11 human subjects. The H reflex facilitation produced by the cutaneous stimulus was smaller when attention was focused on this stimulus than when it was directed to the same cutaneous field on the opposite leg. This demonstrates that selective attention involves specific descending controls on the spinal circuits mediating the segmental effects of cutaneous afferents.

Afferent Pathways↗

PubMed1980

Reduction during movement of the evoked potentials recorded along the extralemniscal pathways of the cat.

Five cats were trained to press a pedal or to stay still. Electrical stimulation was delivered to the skin of the forelimb when the cats stayed still and when they pressed the lever. Gross evoked potentials (EPs) were recorded over the suprasylvian gyrus (ASSG) and in two subcortical non-specific structures: the bulbar nucleus gingantocellularis (NGC) and the centrum medianum of the thalamus (CM). EPs recorded in NGC and over the ASSG showed an early and a late component. In the CM only one component was consistently present in all animals. During the conditioned movement, the EP was reduced in NGC, in CM and over the ASSG. This diminution was statistically significant for the cortical (early and late waves) and the thalamic responses; at the bulbar level the late wave only was diminished. These results are in agreement with the reduction of the cutaneous volley conducted by the lemniscal pathways. The origin and degree of depression of the early and late components are discussed.

Afferent Pathways↗

PubMed1977

Effects of selective attention on the late components of evoked potentials in man.

Vertex and specific evoked potentials to visual and cutaneous stimuli were recorded in 6 subjects. The delivery of roughly equal numbers of flashes and shocks was paced by the subjects themselves. They also had to choose which stimulus they would be given next; 9 times out of 10 the stimulus matched the subject's expectation and stimuli from the unexpected modality were given randomly 1 time out of 10 on the average. No task was required after the stimulus occurrence. Cortical evoked potentials (CEPs) to unexpected stimuli were averaged and compared with CEPs the major difference consisted in large N2 and P3 waves in response to unexpected stimuli; no difference was observed in the amplitude of the N1 wave. In specific CEPs unexpected stimuli also elicited N2 and P3 waves; in addition N1 showed a slight tendency to be higher in CEPs to unexpected stimuli,

Attention↗

PubMed1972