Biomedical subjects

A Riehle

Publications and source records attributed to A Riehle.

28 records · Page 2Linked to original sources

PubMed1994

Neuronal coding of stimulus-response association rules in the motor cortex.

Two monkeys were trained to perform wrist movements to align a pointer with visual targets. In the spatially 'compatible' condition, monkeys had to point at the target position (left/right), whereas in the 'incompatible' condition, they had to point at the position opposite to the target. A large proportion of neurones recorded in the primary motor cortex showed changes in activity according to either the side of the target or the side of the movement. However, more than 40% of neurones changed their activity as a function of the stimulus-response mapping rule. Some of these neurones, being sensitive only to the stimulus-response compatibility effect, must therefore be viewed as specifically involved in the neural mechanisms that control the association process between sensory inputs and motor outputs.

Animals↗

PubMed1994

Spatially modulated touch responses in parietal cortex.

Cortical neurons with low-threshold, cutaneous receptive fields on the fingers were recorded in areas 5 and 7b of the parietal lobe in two awake monkeys, trained in a visually guided reach task. 72% (81/113) of the cells responded when targets displayed on a videomonitor were actively touched. Of these, 20 neurons discharged preferentially when target contact was made on one side of the screen compared with the other. This spatial modulation of the cutaneous modality may have originated in neighboring joint-related neurons which were directionally selective.

Animals↗

PubMed1994

Are extent and force independent movement parameters? Preparation- and movement-related neuronal activity in the monkey cortex.

Movement extent and movement force can be independently controlled in motor performance. Therefore, independent representations of extent and force should exist in the central nervous system (CNS). To test this hypothesis, microelectrode recordings were made in sensorimotor cortex of monkeys trained to perform visually cued wrist flexion movements of two extents, against two levels of frictional resistance. An initial preparatory signal (PS) provided complete, partial or no information about extent and/or force of the movement, which had to be performed in response to a second, response signal (RS). The activity of 511 neurons of the primary motor cortex (MI), the premotor cortex (PM), the postcentral cortex (PC), and the posterior parietal cortex (PA) was recorded in two monkeys. Both reaction time (RT) and neuronal data suggest that there exist independent neuronal mechanisms responsible for the programming of either parameter. On the one hand, partial information about either movement parameter shortened RT when compared with the condition of no prior information. On the other hand, there were, among others, two discrete populations of neurons, one related only to extent, the other only to force. Preparatory changes in activity related to either movement parameter were mainly located in the frontal cortex, especially in the PM. After occurrence of the RS, the percentage of selective changes in activity increased and tended to extend to the parietal cortex. In particular during the movement, force-related changes in activity have been encountered in PA. Furthermore, we conducted trial-by-trial correlation analyses between RT and preparatory neuronal activity for all conditions of prior information. The mean correlation coefficient was significantly higher in the condition of information about movement extent than of information about movement force and it was significantly higher in MI/PM than in PC/PA.

Animals↗

PubMed1993

The predictive value for performance speed of preparatory changes in neuronal activity of the monkey motor and premotor cortex.

Three monkeys were trained in a precued reaction time (RT) paradigm. An initial preparatory signal (PS) provided complete, partial or no information about direction and extent of a wrist flexion/extension movement which was executed after the second, response signal (RS). A PS providing information about direction shortened the RT much more than a PS indicating movement extent. The activity of 464 task-related neurons was recorded in the primary motor (MI) and premotor (PM) cortex. Not only the timing and amplitude of mean activity changes were analyzed, but also trial-by-trial correlation analyses between RT and discharge frequency during the PS-RS interval were conducted. Correlations were stronger in the condition of information about direction than in conditions of information about extent or no information. Considering directionally selective neurons, correlations were stronger when the neuron's preferred direction than the opposite direction was precued. Correlation distributions were similar for MI and PM. Correlations were negative when preparatory activity increased during the PS-RS interval, and positive when activity decreased. Correlation analyses between behavioral performance and neuronal activity can thus be considered as a powerful tool to obtain a deeper insight into the functional mechanism of motor preparation.

Animals↗

PubMed1992

Effects of preliminary perceptual output on neuronal activity of the primary motor cortex.

Observations of single neurons in the primary motor cortex of 1 monkey provided evidence that preliminary perceptual information reaches the motor system before perceptual analysis is complete. Neurons were recorded during a task in which 1 stimulus was assigned to a wrist flexion response and another was assigned to wrist extension. Two stimuli were assigned to a no-go response; each was visually similar to either the flexion or the extension stimulus. When a no-go stimulus was presented, neurons responded with weaker versions of the discharge patterns exhibited to the visually similar stimulus requiring a movement, suggesting that neurons receive partial perceptual information favoring that movement. Functionally separable neuronal populations were identified, and differences in the activations of these provide evidence about the functional effects of preliminary perceptual output on movement control processes.

Animals↗

PubMed1991

Visually induced signal-locked neuronal activity changes in precentral motor areas of the monkey: hierarchical progression of signal processing.

In the precuing paradigm, two successive visual signals were presented to trained monkeys. The first one, the preparatory signal, provided complete, partial or no prior information about parameters, such as direction and extent of the forthcoming wrist movement. After a delay, the illumination of a second visual signal, the response signal, called for execution of the movement and indicated the target. Signal-locked neuronal activity changes, i.e. those which occurred time-locked to the signal onset, were recorded in the premotor cortex and the primary motor cortex of the monkey and classified as selective or non-selective. Selective neurons were defined as those responding to particular information, for instance information about movement direction, provided by the signal, while non-selective neurons responded to all signals irrespective of any contained information. Clear latency differences according to both the selectivity of the neuronal response and the area in which the neuron was recorded could be discerned. The mean latency of non-selective activity changes was significantly shorter than that of selective activity changes. Furthermore, the mean latency of premotor cortical responses was significantly shorter than that of primary motor cortical responses. The data indicate the existence of distinct levels of signal processing from the very general to the highly specific.

Action Potentials↗

PubMed1989

Monkey primary motor and premotor cortex: single-cell activity related to prior information about direction and extent of an intended movement.

1. This study was devoted to the neuronal processes underlying the construction of the motor program. Two monkeys were trained in a choice reaction time task to perform precise wrist flexion and extension movements of small and large extent. During a trial, the first visual signal, the preparatory signal (PS), informed the animal completely, partially, or not at all about direction and/or extent of the forthcoming movement. After a constant waiting period, a second visual signal, the response signal (RS), was illuminated calling for execution of the requested movement. 2. Reaction time (RT) and movement time (MT) measurements during the training as well as the recording sessions revealed that providing prior information about movement parameters strongly affected RT, but only slightly affected MT. Reaction time decreased in relation to the amount (number of movement parameters precued) and the type of prior information. Providing information about movement direction shortened RT much more than providing information about movement extent. Behavioral data support a parametric conception of motor programming, i.e., that the programming of the different movement parameters results from assembling separate processes of different duration. These results are compatible with the model in which programming processes are serially and hierachically ordered, movement direction being processed before movement extent. 3. Single-cell recording techniques were used to study neuronal activity of the primary motor (MI) and the premotor (PM) cortex, contralateral to the active arm. The activity of 155 neurons of MI and 158 neurons of PM was recorded during performance of the task. Of these 313 neurons, only 14 neurons did not change their activity during execution of the task. Two hundred and seven neurons whose activity changes were related to movement direction and/or movement extent have been selected for the further study. They were classified into three main groups: 1) execution-related neurons (49 in MI, 27 in PM), 2) preparation- and execution-related neurons (48 in MI, 54 in PM), and 3) preparation-related neurons (8 in MI, 21 in PM). 4. Directionally selective, execution-related neurons were found to be more frequently located within MI (81/105, 77.1%) than within PM (55/102, 53.9%), whereas directionally selective, preparation-related neurons appeared to be more frequently located within PM (47/102, 46.1%) than within MI (24/105, 22.9%).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Neuronal activity and information processing in motor control: from stages to continuous flow.

Some years ago, we proposed, along with others, that the isomorphism between models of information processing by stages and the organization of neural pathways connecting functionally specialized neuronal networks was a guideline for conducting experiments in which the integration of methods and concepts of cognitive psychology and of neurophysiology was a promising approach to increase our knowledge of the processes responsible for motor control. At a time when models of serially organized information processing stages are being increasingly challenged, the deciphering of the underlying brain processes increasingly suggests that current views about the linkage between neural structures and behavioural functions must be reconsidered. First, at the "molar" level, the notion of a functional specialization of neuronal networks as, for example, being "sensory", "sensorimotor" or "motor", has to be viewed as a quantitative and not as a qualitative concept. Second, at the "molecular" level, the notion of a clear-cut functional differentiation between neuronal units, or between small sets of neurons, must similarly be revised: a neuron may be more or less "sensory" or "motor" and, moreover, may share both these functional properties to varying degrees. When the brain processes responsible for movement control are reconsidered in the light of these two concepts--that is a functional heterogeneity of structurally defined neuronal networks, as well as a continuum in functional specification of isolated neuronal units--data collected by using single-cell recording of neuronal activity fit well into the model of a continuous flow of information processing: neural pathways from the cortical parietal association areas to the corticospinal apparatus appear as a privileged sensorimotor information stream along which the amount of neuronal activity responsible for movement planning progressively decreases, while the amount of neuronal activity involved in movement execution progressively increases.

Animals↗

PubMed1984

Motion detection in flies: parametric control over ON-OFF pathways.

Microscopic illumination of two neighbouring photoreceptor cells within a single ommatidium induces a strong sequence-dependent response in a directionally selective, motion-sensitive neuron. The response is characterized by a strong facilitation in the preferred direction and a weaker inhibition in the reverse direction. The data suggest that for each direction of apparent movement the signal from an ON-OFF pathway is released into the neuron via a parametric control mechanism which is activated by an adjacent channel.

Animals↗

PubMedDate not supplied

Dynamical changes and temporal precision of synchronized spiking activity in monkey motor cortex during movement preparation.

Movement preparation is considered to be based on central processes which are responsible for improving motor performance. For instance, it has been shown that motor cortical neurones change their activity selectively in relation to prior information about movement parameters. However, it is not clear how groups of neurones dynamically organize their activity to cope with computational demands. The aim of the study was to compare the firing rate of multiple simultaneously recorded neurones with the interaction between them by describing not only the frequency of occurrence of epochs of significant synchronization, but also its modulation in time and its changes in temporal precision during an instructed delay. Multiple single-neurone activity was thus recorded in monkey motor cortex during the performance of two different delayed multi-directional pointing tasks. In order to detect conspicuous spike coincidences in simultaneously recorded spike trains by tolerating temporal jitter ranging from 0 to 20 ms and to calculate their statistical significance, a modified method of the 'Unitary Events' analysis was used. Two main results were obtained. First, simultaneously recorded neurones synchronize their spiking activity in a highly dynamic way. Synchronization becomes significant only during short periods (about 100 to 200 ms). Several such periods occurred during a behavioural trial more or less regularly. Second, in many pairs of neurones, the temporal precision of synchronous activity was highest at the end of the preparatory period. As a matter of fact, at the beginning of this period, after the presentation of the preparatory signal, neurones significantly synchronize their spiking activity, but with low temporal precision. As time advances, significant synchronization becomes more precise. Data indicate that not only the discharge rate is involved in preparatory processes, but also temporal aspects of neuronal activity as expressed in the precise synchronization of individual action potentials.

Animals↗