Emergence of Bursting Activity in Connected Neuronal Sub-Populations

Uniform and modular primary hippocampal cultures from embryonic rats were grown on commercially available micro-electrode arrays to investigate network activity with respect to development and integration of different neuronal populations. Modular networks consisting of two confined active and inter-connected sub-populations of neurons were realized by means of bi-compartmental polydimethylsiloxane structures. Spontaneous activity in both uniform and modular cultures was periodically monitored, from three up to eight weeks after plating. Compared to uniform cultures and despite lower cellular density, modular networks interestingly showed higher firing rates at earlier developmental stages, and network-wide firing and bursting statistics were less variable over time. Although globally less correlated than uniform cultures, modular networks exhibited also higher intra-cluster than inter-cluster correlations, thus demonstrating that segregation and integration of activity coexisted in this simple yet powerful in vitro model. Finally, the peculiar synchronized bursting activity shown by confined modular networks preferentially propagated within one of the two compartments (‘dominant’), even in cases of perfect balance of firing rate between the two sub-populations. This dominance was generally maintained during the entire monitored developmental frame, thus suggesting that the implementation of this hierarchy arose from early network development.     

Motor Activity Improves Temporal Expectancy

Certain brain areas involved in interval timing are also important in motor activity. This raises the possibility that motor activity might influence interval timing. To test this hypothesis, we assessed interval timing in healthy adults following different types of training. The pre- and post-training tasks consisted of a button press in response to the presentation of a rhythmic visual stimulus. Alterations in temporal expectancy were evaluated by measuring response times. Training consisted of responding to the visual presentation of regularly appearing stimuli by either: (1) pointing with a whole-body movement, (2) pointing only with the arm, (3) imagining pointing with a whole-body movement, (4) simply watching the stimulus presentation, (5) pointing with a whole-body movement in response to a target that appeared at irregular intervals (6) reading a newspaper. Participants performing a motor activity in response to the regular target showed significant improvements in judgment times compared to individuals with no associated motor activity. Individuals who only imagined pointing with a whole-body movement also showed significant improvements. No improvements were observed in the group that trained with a motor response to an irregular stimulus, hence eliminating the explanation that the improved temporal expectations of the other motor training groups was purely due to an improved motor capacity to press the response button. All groups performed a secondary task equally well, hence indicating that our results could not simply be attributed to differences in attention between the groups. Our results show that motor activity, even when it does not play a causal or corrective role, can lead to improved interval timing judgments.     

Motor Activity of Eyelids as a Functional State Indicator

The authors consider an insufficiently studied indicator, i.e., motor activity of eyelids, recorded with or without miniature contacts in infrared rays for the visual analyzer states eyes open / eyes closed. Eyelid movement characteristics are highly informative in diagnosing the functional state and evaluating operator activity quality under monotonous conditions. The authors discuss possible mechanisms of the influence of such functional states on the motor activity of eyelids.     

Time-Dependent Effects of Trichloroethylene on Motor Activity in Rats

Circadian variations in acute and subacute neurobehavioural effects of trichloroethylene (TRI: 1.2 g/kg i.p.) were investigated in the rat under a light: dark = 12:12 hr cycle. An acute effect of TRI evaluated by decreased muscle tone was maximal during the early dark phase (21:00). A subacute effect of TRI was evaluated by a continuous recording of spontaneous locomotor activity in the rat. The circadian rhythm in spontaneous locomotor activity was extensively impaired by the injection of TRI for three consecutive days. Spectral analysis of spontaneous locomotor activity showed that ultradian periods became more dominant than the circadian period, and the 1//fluctuation of the spectrum disappeared after the injection of TRI. The effect of TRI on the circadian rhythm in spontaneous locomotor activity was circadian-phase dependent, and the treatment of TRI at 09:00 provoked greater circadian rhythm impairment than that at 21:00. The mechanisms of the time-dependent effect of TRI on neurobehaviour are the subject of further investigation.     

Time-Dependent Effects of Trichloroethylene on Motor Activity in Rats

Circadian variations in acute and subacute neurobehavioural effects of trichloroethylene (TRI: 1.2 g/kg i.p.) were investigated in the rat under a light: dark = 12:12 hr cycle. An acute effect of TRI evaluated by decreased muscle tone was maximal during the early dark phase (21:00). A subacute effect of TRI was evaluated by a continuous recording of spontaneous locomotor activity in the rat. The circadian rhythm in spontaneous locomotor activity was extensively impaired by the injection of TRI for three consecutive days. Spectral analysis of spontaneous locomotor activity showed that ultradian periods became more dominant than the circadian period, and the 1//fluctuation of the spectrum disappeared after the injection of TRI. The effect of TRI on the circadian rhythm in spontaneous locomotor activity was circadian-phase dependent, and the treatment of TRI at 09:00 provoked greater circadian rhythm impairment than that at 21:00. The mechanisms of the time-dependent effect of TRI on neurobehaviour are the subject of further investigation.     

Coupled Spike Activity in Micropopulations of Motor Cortex Neurons in Rats

Using eight-channel metal microelectrodes (diameter of a separate channel 12 μm), we extracellularly recorded the impulse activity of 186 single neurons or their small groups (usually, pairs) localized in the motor cortex of rats anesthetized with ketamine. In 60 cases (32.3%), action potentials (APs) of two single neurons were generated in a parallel manner and demonstrated fixed time relations with each other. This is interpreted as being a result of excitation of two neighboring functionally connected (coupled) cells. These AP pairs could be recorded via one and the same or two neighboring microelectrode channels. Second APs in the pair were elicited exclusively in the case where an AP was preliminarily generated by another neuron, while APs of the latter in some cases could arrive independently. Therefore, “leading” and “accompanying” cells could be identified in such neuronal pairs. The coupling coefficient in the generation of APs by an accompanying unit with respect to APs generated by a leading cell was close to 100%, with no dependence on the discharge frequency in the latter. Intervals between APs of two neurons in different coupled pairs varied from about 1.0 to 22-23 msec. In the case of minimum values of these interspike intervals, APs generated by coupled neurons overlapped each other; this resulted in the formation of spikes looking like “complex APs.” Within some time intervals, interspike intervals could increase, and such APs began to be decomposed. The above-described data are considered electrophysiological proof of the existence of tight functional coupling between a significant part of cortical neurons spatially close to each other, i.e., members of a micropopulation, which was obtained in an in vivo experiment.     

Suppression of Abdominal Motor Activity during Swallowing in Cats and Humans

Diseases affecting pulmonary mechanics often result in changes to the coordination of swallow and breathing. We hypothesize that during times of increased intrathoracic pressure, swallow suppresses ongoing expiratory drive to ensure bolus transport through the esophagus. To this end, we sought to determine the effects of swallow on abdominal electromyographic (EMG) activity during expiratory threshold loading in anesthetized cats and in awake-healthy adult humans. Expiratory threshold loads were applied to recruit abdominal motor activity during breathing, and swallow was triggered by infusion of water into the mouth. In both anesthetized cats and humans, expiratory cycles which contained swallows had a significant reduction in abdominal EMG activity, and a greater percentage of swallows were produced during inspiration and/or respiratory phase transitions. These results suggest that: a) spinal expiratory motor pathways play an important role in the execution of swallow, and b) a more complex mechanical relationship exists between breathing and swallow than has previously been envisioned.     

A Method for Recording the Motor Activity of the Reticulum in Cattle

A method for recording the motility of the reticulum in normal cattle has been devised. The method is based on measurement of the pressure variations occurring in connection with the reticular contractions. The pressure is transferred through open, water-filled catheters via a pressure transducer to an electromanometer, from which it is recorded with the aid of a mingograf. Mean values for the interval, duration and amplitude of the reticular contractions in 10 normal cows are given. The method permits recording in intact animals without any preliminary measures, and can therefore be used in clinical cases.     

From Spontaneous Motor Activity to Coordinated Behaviour: A Developmental Model

In mammals, the developmental path that links the primary behaviours observed during foetal stages to the full fledged behaviours observed in adults is still beyond our understanding. Often theories of motor control try to deal with the process of incremental learning in an abstract and modular way without establishing any correspondence with the mammalian developmental stages. In this paper, we propose a computational model that links three distinct behaviours which appear at three different stages of development. In order of appearance, these behaviours are: spontaneous motor activity (SMA), reflexes, and coordinated behaviours, such as locomotion. The goal of our model is to address in silico four hypotheses that are currently hard to verify in vivo: First, the hypothesis that spinal reflex circuits can be self-organized from the sensor and motor activity induced by SMA. Second, the hypothesis that supraspinal systems can modulate reflex circuits to achieve coordinated behaviour. Third, the hypothesis that, since SMA is observed in an organism throughout its entire lifetime, it provides a mechanism suitable to maintain the reflex circuits aligned with the musculoskeletal system, and thus adapt to changes in body morphology. And fourth, the hypothesis that by changing the modulation of the reflex circuits over time, one can switch between different coordinated behaviours. Our model is tested in a simulated musculoskeletal leg actuated by six muscles arranged in a number of different ways. Hopping is used as a case study of coordinated behaviour. Our results show that reflex circuits can be self-organized from SMA, and that, once these circuits are in place, they can be modulated to achieve coordinated behaviour. In addition, our results show that our model can naturally adapt to different morphological changes and perform behavioural transitions.     

On the Interrelationship of Speech Functioning and Manual Motor Activity in Aphasia

Clinicians, physiologists, and psychologists are familiar with cases of simultaneous disturbance of various functions in localized cerebral lesions. These phenomena have been studied and described repeatedly, but continue to be of substantial interest, as analysis of them may make a contribution to the study of localization of functions in the cerebral cortex, substitution and restoration of functions, and the nature of their interrelationships. Our attention was attracted by a case of simultaneous disturbance of motor function and the power of speech in a lesion of the left (dominant) hemisphere. We began by investigating motor functions in aphasia and in the normal state, with a view to subsequent comparison of the motor and verbal functions in the normal state and in aphasia.     

Self-Initiated Motor Behavioral Act-Related Neuronal Activity in the Cat Locus Coeruleus

In experiments on awake cats, we recorded the activity of 61 putative noradrenergic neurons localized within the region of the locus coeruleus (LC) of the brainstem. The animals were trained to perform a self-initiated (voluntary) motor act aimed at obtaining a food reward by pushing a pedal by the forelimb. The intervals between pushings (stay of the limb on a platform before initiation of the movement) should not be shorter than 4 sec, and the duration of the movement itself should not exceed 1 sec. The following impulse reactions were most clearly manifested (i) related to the pre-starting events and performance of the voluntary movement, (ii) related to the presentations of the conditioning stimuli, which predicted giving out the food reward (a positive signal) or the absence of the latter (a negative signal) and (iii) related to the reward presentation. About 50% of the LC units under study had changed their activities before the movement was initiated. These reactions can be related to a cognitive component (determination of the movement initiation(, which is present in the experimental task. Most neurons responded by phasic activation to presentation of the conditioning signals, and this activation was more pronounced in the case of negative signals. Responses of the studied nerve cells are probably indicative of the involvement of the LC neuronal systems in the perception of the emotiogenic stimuli, as well as in the processes providing the maintenance of selective attention within different stages of targeted behavioral acts.     

Heart Rate Variability in Subjects with Increased Motor Activity and Athletes

Heart rate variability (HRV) was assessed with a NeiroSoft hardware and software complex in 303 subjects, including subjects with increased motor activity and athletes. Factor analysis was used to reveal the most informative HRV indices, which accounted for two-thirds of the generalized variance of the indices under study, evidencing a balanced and orderly state of the body in subjects with increased motor activity and athletes and the improvement of neurohumoral and autonomic control of motor functions.     

Successful Reconstruction of a Physiological Circuit with Known Connectivity from Spiking Activity Alone

Identifying the structure and dynamics of synaptic interactions between neurons is the first step to understanding neural network dynamics. The presence of synaptic connections is traditionally inferred through the use of targeted stimulation and paired recordings or by post-hoc histology. More recently, causal network inference algorithms have been proposed to deduce connectivity directly from electrophysiological signals, such as extracellularly recorded spiking activity. Usually, these algorithms have not been validated on a neurophysiological data set for which the actual circuitry is known. Recent work has shown that traditional network inference algorithms based on linear models typically fail to identify the correct coupling of a small central pattern generating circuit in the stomatogastric ganglion of the crab Cancer borealis. In this work, we show that point process models of observed spike trains can guide inference of relative connectivity estimates that match the known physiological connectivity of the central pattern generator up to a choice of threshold. We elucidate the necessary steps to derive faithful connectivity estimates from a model that incorporates the spike train nature of the data. We then apply the model to measure changes in the effective connectivity pattern in response to two pharmacological interventions, which affect both intrinsic neural dynamics and synaptic transmission. Our results provide the first successful application of a network inference algorithm to a circuit for which the actual physiological synapses between neurons are known. The point process methodology presented here generalizes well to larger networks and can describe the statistics of neural populations. In general we show that advanced statistical models allow for the characterization of effective network structure, deciphering underlying network dynamics and estimating information-processing capabilities.     

A Psychological Study of the Development of Motor Activity in the Preschool-Age Child

During the period from 4 to 6 years, the preschooler's motor activity becomes stronger and hardier, and his movements become more dextrous and coordinated. During this period a child also acquires a number of new motor skills that will play an important role in later life. Finally, he learns to execute movements consciously and deliberately.     

Asymmetrical Effect of Levodopa on the Neural Activity of Motor Regions in PD

Parkinson''s disease (PD) is a neurodegenerative illness often characterized by asymmetrical symptoms. However, the reason for this asymmetry and the cerebral correlates underlying symptom asymmetry are still not well understood. Furthermore, the effects of levodopa on the cerebral correlates of disease asymmetry have not been investigated. In this study, right-handed PD patients performed self-initiated, externally triggered and repetitive control finger movements with both their right and left hands during functional magnetic resonance imaging (fMRI) to investigate asymmetrical effects of levodopa on the hemodynamic correlates of finger movements. Patients completed two experimental sessions OFF and ON medication after a minimum of 12 hours medication withdrawal. We compared the effect of levodopa on the neural activation patterns underlying the execution of both the more affected and less affected hand for self-initiated and externally triggered movements. Our results show that levodopa led to larger differences in cerebral activity for movements of the more affected, left side: there were significant differences in activity after levodopa administration in regions of the motor cortico-striatal network when patients performed self-initiated and externally triggered movements with their left hand. By contrast, when patients used their right hand, levodopa led to differences in cerebellar activity only. As our patients were affected more severely on their left side, we propose that levodopa may help provide additional dopaminergic input, improving movements for the more severely affected side. These results suggest that the impact of reduced dopamine in the cortico-striatal system and the action of levodopa is not symmetrical.     

Stability of Adult Emergence and Activity/Rest Rhythms in Fruit Flies Drosophila melanogaster under Semi-Natural Condition

Here we report the results of a study aimed at examining stability of adult emergence and activity/rest rhythms under semi-natural conditions (henceforth SN), in four large outbred fruit fly Drosophila melanogaster populations, selected for emergence in a narrow window of time under laboratory (henceforth LAB) light/dark (LD) cycles. When assessed under LAB, selected flies display enhanced stability in terms of higher amplitude, synchrony and accuracy in emergence and activity rhythms compared to controls. The present study was conducted to assess whether such differences in stability between selected and control populations, persist under SN where several gradually changing time-cues are present in their strongest form. The study revealed that under SN, emergence waveform of selected flies was modified, with even more enhanced peak and narrower gate-width compared to those observed in the LAB and compared to control populations in SN. Furthermore, flies from selected populations continued to exhibit enhanced synchrony and accuracy in their emergence and activity rhythms under SN compared to controls. Further analysis of zeitgeber effects revealed that enhanced stability in the rhythmicity of selected flies under SN was primarily due to increased sensitivity to light because emergence and activity rhythms of selected flies were as stable as controls under temperature cycles. These results thus suggest that stability of circadian rhythms in fruit flies D. melanogaster, which evolved as a consequence of selection for emergence in a narrow window of time under weak zeitgeber condition of LAB, persists robustly in the face of day-to-day variations in cycling environmental factors of nature.