Biomedical subjects

Franck Vidal

Publications and source records attributed to Franck Vidal.

5 recordsLinked to original sources

PubMed2002

An additive factor analysis of the effect of sub-anaesthetic doses of nitrous oxide on information processing: evidence for an impairment of the motor adjustment stage.

RATIONALE: Nitrous oxide (N(2)O) inhalation, at subanaesthetic concentrations, impairs choice reaction time (RT). However, the functional locus of this effect remains to be ascertained. In the present study, this issue was investigated by applying the additive factor logic to the RTs of rats performing a visuo-motor task. METHOD: The task consisted of either a left-side or a right-side body displacement to a visual stimulus displayed in either the left or right hemispace. The experimental design involved the manipulation of two task factors (stimulus luminance and foreperiod duration) the effects of which are additive on RT. Inhaled N(2)O (from 0% to 60%) was varied as the third factor of the design. RESULTS: N(2)O prolonged RT in a dose-dependent manner and this effect was additive with that of stimulus luminance, whilst it interacted with that of foreperiod duration. Moreover, at low concentrations (10-20%), N(2)O abolished the effect of foreperiod, possibly through a disturbance of time estimation processes, whereas at higher concentrations (30-40%) N(2)O enhanced the effect of foreperiod, probably by slowing down motor processes. Movement time (MT) was decreased by N(2)O at 20-40%. CONCLUSIONS: The present data provide evidence that N(2)O impairs information processing by altering at least the stage of motor adjustment. In addition, N(2)O spares the sensory processes implemented during the stimulus preprocessing stage. A subsidiary result is that at some concentrations, N(2)O displays opposite effects on reaction time and movement time. These results demonstrate that the additive factor method constitutes a powerful new tool for studying the pharmacology of information processing in animal models.

Anesthetics, Inhalation↗

PubMed2002

Executive control in the Simon effect: an electromyographic and distributional analysis.

Manual responses to lateralized stimuli are faster for spatially congruent stimulus-response associations than for incongruent associations, even if the stimulus location is irrelevant. This effect, however, decreases as reaction time increases. Recent data suggest that such a decrease reflects online, within-trial executive control. The present study was aimed at testing this hypothesis by analyzing the electromyographic activity of muscles involved in response execution. We focused on the particular trials in which an activation of the muscle involved to the incorrect response preceded the execution of the correct response. A sequential effect analysis, along with an analysis of the reaction time distributions, revealed that after such dual-activation trials, executive control was reinforced. In addition, a distribution analysis of the reaction times associated with such trials compared to the trials without incorrect activation, revealed online, within-trial changes in executive control. Arguments against a late motor locus of the effect of the irrelevant stimulus location are also provided. These results are discussed in terms of current models of cognitive control.

Adolescent↗

PubMed2002

Time processing reflected by EEG surface Laplacians.

We previously described significant relationships between amplitude variations in slow brain potentials and timed between-press intervals (2.5 s). We suggested that these variations are neural traces of timing mechanisms. To determine which time processing stage is concerned, the current study examines whether these variations result from trial-to-trial memory updating controlled by feedback or from memory consolidation. EEG surface Laplacians (SL) were computed from the first trial on, with feedback (condition 1) and after feedback suppression (condition 2). Performance-dependent variations were related to the individual memory traces revealed by condition 2. As in our previous data, they were restricted to a site overlying the supplementary motor area (SMA). The data suggest that the SMA subserves timing functions, involving memory consolidation and cumulative activation processes as described by current models.

Adult↗

PubMed2002

A transcranial magnetic stimulation study of information processing in the motor cortex: relationship between the silent period and the reaction time delay.

The present study was aimed at deciphering whether the delay in choice reaction time (RT) and the silent period (SP) caused by transcranial magnetic stimulation (TMS) of the motor cortex in the ongoing electromyogram are due to the same physiological mechanism. To this end, the effect of TMS was studied in 6 healthy volunteers performing a between-hand choice RT task. Specific predictions were derived from a logic inspired from the "postponed stages" hypothesis (Pashler & Johnson, 1989). This logic predicts a correlation between SP duration and RT when the stimulated cortex is involved in the response, and a stronger correlation when the stimulation is delivered later during the RT interval. The effect of TMS on RT was twofold: At early stimulation times, the stimulation shortened the RT and this effect was independent of the involvement of the stimulated motor cortex in the subsequent response. At later stimulation times, TMS had a disruptive effect, provided that the stimulated cortex was involved in the response. When the stimulated cortex was involved in the response, there was a correlation between SP and RT; this correlation was stronger when the stimulation occurred later. In contrast, there was no correlation between these two variables when the stimulated cortex was not involved.

Adult↗

PubMed2002

[Treatment dynamics in sensorimotor disorders: the contribution of electrophysiology].

In the field of sensorimotor activities, progresses achieved over the last fifty years have been largely driven by the Reaction Time (RT) paradigm. Information processing models are set in the context of a global breakdown of sensorimotor activities in multiple concatenated stages, each aggregated in many fundamental operations that are functionally linked. If there is a consensus today about this breakdown, the way stages organize themselves in time however is still much debated. According to one hypothesis, there is no temporal overlap between each stages: the process occurs sequentially. According to another theory, the stages overlap over in time: the process occurs in a parallel manner. A behavioral analysis does not allow to determine between these two hypothesis because the RT represents the final product of the whole sensorimotor pathway, while the temporal organization of the processing of information depends on the nature of the transfer between individual stages. An all-or-nothing information transfer, also called discrete, leads to a sequential organization, while a progressive or continuous transfer brings about a parallel organization. Moreover, contrary to a preconceived notion, data obtained from classical neurophysiology are compatible with both a sequential organization and a parallel organization. Particularly, the great number of connections between the different elements of the nervous system has often seemed difficult to conciliate with a sequential organization. In fact, this argument is inadmissible because it stems from confusion between a temporal organization and an anatomical organization of the processing of information. More generally, our knowledge of the functional anatomy of sensorimotor activities imposes but few constraints on the temporal organization patterns of the processing of information. The lack of interest for the neurophysiological argument seems essentially due to the fact that theses arguments rest on research which is not aimed at the temporal organization of the sensorimotor information processing. Recently, approaches that integrate concepts and methods used in experimental psychology and neurosciences have contributed to putting in perspective the organization of information processing. Electromyography, EEG, reflexology and neuronal recording techniques have been used in the context of two inference logics. The first logic, that we call "factual", is based on the study of functional relations between RT and certain neuronal events. The second logic, that we call "chronometric", is based on the study of the relationships between RT and intervals resulting from the breakdown of the RT in relation to certain neuronal events. Generally speaking, most studies suggest that in tasks where the stimulus is composed of numerous attributes, information processing operates in parallel. On the other hand, when the stimulus is made up of a single attribute, information processing could be operating in a sequential manner. One weakness of this electrophysiological approach is that it has so far only examined relationships between physiological indicators and means RT. We propose here to offset these weaknesses by examining functional relationships between RT distribution variances and certain neuronal events linked to information processing.

Electrophysiology↗