Noradrenergic modulation of tactile responses in rat cortex. Current source-density and unit analyses.

This study describes the noradrenergic modulation of tactile afferent information in the sensorimotor cortex of urethane-anesthetized rats. Synaptic and spike responses to a mechanical stimulation of the hand palm were evaluated by means of current source-density analysis and unit activity recording in all cortical layers. Results showed that activation of the locus coeruleus decreased and shortened afferent synaptic excitation in supragranular, but not in deep layers. On the average, unit responses exhibited facilitated latency, moderately increased amplitude, enhanced postexcitatory inhibition and synchronization of responses across layers. The apparent paradox of this global phasic facilitation correlated with a decrease in input synaptic currents was discussed according to hypotheses which might explain its functional significance.

A versatile software system for controlling various within-subject tasks in behaving monkeys and humans: application to an attention task.

A multi-purpose software system is described for controlling a variety of tasks used in experiments on behaving monkeys and humans. It involved two programs, a real-time unit and a task editor. The former used editable pixel maps flashed on a computer screen as visual stimuli and operated according to a control list of trial parameters specifying the various components of each trial in the behavioural session. It involved an interrupt-driven driver interface for clock control and response analysis, and a main code managing the session process, disk access and stimulus display. The task editor was used to generate the list of trial parameters and edit the pixel-map of signals. It generated a task file used by the real-time unit. Experimental manipulations could be implemented through the organisation of the behavioural session by trial types corresponding to the different behavioural conditions. The system's capabilities are illustrated by behavioural results from an attention task in which monkeys increased their attention as a function of task difficulty.

Prefrontal neurones sensitive to increased visual attention in the monkey.

Single units were recorded in the prefrontal cortex of two monkeys performing a simple visual detection task. Task difficulty was manipulated in consecutive blocks of trials to increase the degree of attention towards the stimulus. Fifteen percent of the neurones sampled exhibited a systematic change in the average preparatory discharge rate in relation to task difficulty. Behavioural data (changes in reaction time and error ratios, 'difficult' probe trials presented in the 'easy' context) suggested that increased attention was actually induced. These results show the sensitivity of a population of prefrontal neurones to the behavioural context which determine the level of attention. The preparatory nature of the observed changes may be of special functional significance for the control of effortful attention.

A comparison of preparation-related neuronal activity changes in the prefrontal, premotor, primary motor and posterior parietal areas of the monkey cortex: preliminary results.

Single-unit activity of prefrontal (PF), premotor (PM), primary motor (MI) and posterior parietal (PP) cortical areas was analysed from 3 monkeys trained to perform visually guided arm movements in a between-arms choice reaction time (RT) task. Percentages of preparation-related units, i.e. units whose change in activity during the preparatory period was correlated with RT, were 19% in PF, 31% in MI, 46% in PM and 68% in PP, respectively. These data support the hypothesis that neural pathways connecting PP association areas to MI, via PM, are involved mainly in movement planning.

Changes in neuronal activity of the monkey precentral cortex during preparation for movement.

The aim of this study was to analyze the changes in neuronal activity of the motor cortex associated with preparation for movement. Monkeys were trained to perform a between-hands choice-reaction time (RT) task. They pressed upon two levers with both hands and, after a preparatory period of 1-s duration initiated by a warning tone, they must point at either a left- or right-located target, when illuminated as a response signal, with either the left or right hand. The level of preparation for performing either sided movement was changed by manipulating, across block of trials, the relative probabilities for the left and right hands to point at the corresponding target. When considering behavioral data averaged over daily sessions, it was found that RT significantly decreased as response probability increased, whereas movement time (MT) was not affected. However, large changes in this rule were observed when data collected within a single session were considered. Response probability manipulation was acting on RT alone in 27% of sessions, on MT alone in 19% of sessions, and on both RT and MT in 17% of sessions. Statistically significant trial-by-trial correlations between RT and MT were found; of positive sign for 34% of sessions and of negative sign for 12% of sessions. Electromyographic recordings from the biceps and triceps brachii showed that muscle activity remained stable during the preparatory period, both muscles of the performing arm began to be coactivated about 70-130 ms before the lever release, biceps activation being progressively larger than that of the triceps, and the rising slope of biceps activation was steeper for short than for long RTs. Single-cell recording techniques were used to study the neuronal activity of primary motor cortex during the performance of the task. One hundred and fifteen units in area 4, whose activity was recorded during a whole experimental session, were selected for further analysis. Disregarding 4% of units which did not exhibit any movement-related change in activity, it was found that twenty-one percent of units were related to contralateral movements only, 2% to ipsilateral movements only, and 73% to both sided movements. Among this last subset, 27% of units exhibited reciprocal movement-related changes in activity, the most often an excitation for contralateral movements and an inhibition for ipsilateral movements, and 50% of units exhibited a movement-related change in activity in the same direction for both movements, the most often an excitation.(ABSTRACT TRUNCATED AT 400 WORDS)

Head movements and actographic recordings in free-moving animals, using computer analysis of video images.

A method is described to record the X,Y-coordinates of two bright spots on a TV image. These spots are produced by a light-emitting diodes (LEDs) assembly, which must be affixed on the moving target. The system was developed to record head movements of free-moving animals, chronically implanted to bear a socket LEDs holder, but it can be easily adapted to other applications, such as the measure of limb displacements in Man. Recordings are allowed up to 25 frames per second with an approximate spatial resolution of 255(X) X 300(Y). The method, which is based on standard TV equipment, involves a hardware interface, feeding the X and Y counts into a laboratory minicomputer and data acquisition software. A sample record is shown and other applications are discussed in relation to current non-video and video actographic techniques.

Duration of paradoxical sleep episodes. A quantitative and pattern analysis of reticular multi-unit activity in the cat.

This study was aimed at the possible relationships between the level of brain activation in PS and the duration of episodes. Multi-unit activities from 16 recording sites in the mesencephalic and pontine structures were quantitatively evaluated in five cats and the influence of electrode localization and episode duration on the average patterns of integrated discharges was statistically investigated. The analyses emphasized the slow time course of the early increments in reticular activity and its culmination at a plateau level in the later part of PS phases. Differences in mean amplitude of this plateau were related to the anatomical localization of electrodes but no distinction could be made between reticular areas with respect to the temporal features of activation patterns. Synchronization of phasic bursts was consistently observed between simultaneously recorded structures and this, along with the time course of early increments in SW was consistent with the notion that mesencephalic reticular activity is controlled by leading influences from the pons. No basic differences in the temporal development of reticular activation in PS were found in relation to the duration of episodes.

Changes in paradoxical sleep accompanying instrumental learning in the cat.

Five animals were used as their own controls for a replication on cats of earlier findings of facilitated paradoxical sleep (PS) after learning. The experiment was based on an instrumental conditioning with positive reinforcement and three-hour recordings of the subsequent sleep. Facilitation was observed as (a) an increase in the amount of PS during the first 45 min of sleep, (b) an increase in PS episode duration, (c) a decrease in PS latencies and (d) a decrease in slow wave duration versus PS episode duration in the early sleep cycles. The lengthening of PS phases was the only change closely correlated with the state of acquisition.