Control and synchronization of laser bursting and its implications in neuroscience

We present experimental and numerical evidence of control and synchronization of burst events in modulated CO₂ lasers. Bursts appear randomly in each laser as trains of large amplitude spikes intercalated by a small amplitude chaotic regime. Experimental data and model display the frequency locking of bursts in a suitable interval of coupling strengths. The analogy with neuronal bursting will also be discussed in view of the role of bursting synchronization in cognitive functions.     

A mechanism for elliptic-like bursting and synchronization of bursts in a map-based neuron network

A system consisting of two Rulkov map-based neurons coupled through reciprocal electrical synapses as a simple phenomenological example is discussed. When the electrical coupling is excitatory, the square-wave bursting can be well predicted by the bifurcation analysis of a comparatively simple low-dimensional subsystem embedded in the invariant manifold. While, when the synapses are inhibitory due to the artificial electrical coupling, a fast–slow analysis is carried out by treating the two slow variables as two different bifurcation parameters. The main result of this paper is to present a mechanism for the occurrence of a kind of special elliptic bursting. The mechanism for this kind of elliptic-like bursting is due to the interaction between two chaotic oscillations with different amplitudes. Moreover, the generation of antiphase synchronization of networks lies in the different switching orders between two pairs of different chaotic oscillations corresponding to the first neuron and the second neuron, respectively.     

A mechanism for elliptic-like bursting and synchronization of bursts in a map-based neuron network

A system consisting of two Rulkov map-based neurons coupled through reciprocal electrical synapses as a simple phenomenological example is discussed. When the electrical coupling is excitatory, the square-wave bursting can be well predicted by the bifurcation analysis of a comparatively simple low-dimensional subsystem embedded in the invariant manifold. While, when the synapses are inhibitory due to the artificial electrical coupling, a fast–slow analysis is carried out by treating the two slow variables as two different bifurcation parameters. The main result of this paper is to present a mechanism for the occurrence of a kind of special elliptic bursting. The mechanism for this kind of elliptic-like bursting is due to the interaction between two chaotic oscillations with different amplitudes. Moreover, the generation of antiphase synchronization of networks lies in the different switching orders between two pairs of different chaotic oscillations corresponding to the first neuron and the second neuron, respectively.     

Inter-limb coupling in individuals with transtibial amputation during bilateral stance is direction dependent

We investigated the control of upright standing in individuals with unilateral transtibial amputation (TTA) by assessing the inter-limb coupling and the coupling between the center of pressure beneath both limbs combined (COP_NET) and the center of pressure (COP) beneath the prosthetic limb and the intact limb. Twenty-one adults with TTA and eighteen unimpaired adults completed 90 s of standing on two parallel force plates. The inter-limb coupling and the coupling between the COP beneath each limb and the COP_NET were assessed by quantifying the synchronization of the COP signals. This included the number of epochs with synchronized signals, the total duration of signal synchronization and the relative phase and deviation phase between the signals. Additionally, magnitude and temporal characteristics of the COP displacements were quantified. Individuals with TTA exhibited looser inter-limb coupling in the anterior-posterior direction, characterized by more shifts between epochs with synchronized signals, shorter total duration of signal synchronization, less in-phase coordination patterns and a higher deviation phase between the two limbs, compared to unimpaired individuals. This coincided with a larger and more irregular postural sway in the TTA group. No group difference was observed in the mediolateral direction. The coupling between the COP_NET and the COP beneath the individual limbs was similarly direction dependent, and tighter for the intact side, suggesting that an intact limb-driven strategy was utilized.     

Computer signal detection by monitoring auditory evoked potentials

A digital computer, using a simple decision algorithm, attempted to determine when an acoustical signal had been presented to a cat by monitoring the amplitude of the evoked potentials (EP) at brainstem auditory nuclei. The signal-to-noise level at threshold and the shape and range of the decision model “psychometric functions” were similar to those obtained from humans in the same task. In addition, the detection performance obeys Weber’s law, the mean amplitude of the EP increases monotmonically with signal level, the variance of the amplitude is independent of both signal and noise level, and both the mean latency and the variance of the latency of the peaks decrease with increasing signal level. These findings suggest that the synchronization in firing of a population of single units plays a part in determining the amplitude of the EP. Interaural effects in detection performance were found at the inferior colliculus and, to a lesser extent, at the superior olive.     

Spike synchronization of chaotic oscillators as a phase transition

We study how a locally coupled array of spiking chaotic systems synchronizes to an external driving in a short time. Synchronization means spike separation at adjacent sites much shorter than the average inter-spike interval; a local lack of synchronization is called a defect. The system displays sudden spontaneous defect disappearance at a critical coupling strength suggesting an existence of a phase transition. Below critical coupling, the system reaches order at a definite amplitude of an external input; this order persists for a fixed time slot. Thus, the array behaves as an excitable-like system, even though the single element lacks such a property.     

Spike synchronization of chaotic oscillators as a phase transition

We study how a locally coupled array of spiking chaotic systems synchronizes to an external driving in a short time. Synchronization means spike separation at adjacent sites much shorter than the average inter-spike interval; a local lack of synchronization is called a defect. The system displays sudden spontaneous defect disappearance at a critical coupling strength suggesting an existence of a phase transition. Below critical coupling, the system reaches order at a definite amplitude of an external input; this order persists for a fixed time slot. Thus, the array behaves as an excitable-like system, even though the single element lacks such a property.     

A cellular analogue of operant conditioning.

Using the hippocampal-slice preparation, we attempted to model operant conditioning in vitro by reinforcing pyramidal cell bursting responses with local micropressure applications of transmitters and drugs. The same injections were administered independently of bursting to provide a "noncontingent" control for direct pharmacological stimulation or facilitation of firing. The results suggested that the bursting responses of individual CA1 pyramidal neurons may be reinforced in a dose-related manner by response-contingent (but not noncontingent) injections of dopamine and the selective dopamine D2 agonist, N-0923. N-0924, a stereoisomer of N-0923 that is largely devoid of D2-agonist activity, failed to reinforce CA1 bursting. Burst-contingent injections of the excitatory neurotransmitter glutamate also failed to reinforce CA1 bursting; indeed, the glutamate applications (whether contingent or random) reduced the likelihood of bursts while increasing the frequency of solitary spikes. Reinforcement delays exceeding 200 ms largely eliminated the reinforcing efficacy of the D2 agonist N-0437 in CA1 operant conditioning. The results are consistent with the suggestion that the behaviorally reinforcing effects of dopaminergic agents can be modeled in vitro in the hippocampal-slice preparation.     

Slow potential changes and choice reaction time as a function of interstimulus interval

Slow potential changes were recorded over the vertex (C_z) during a choice reaction task. The constant interstimulus interval (ISI) between the visual warning (S₁) and the visual imperative signal (S₂) was either 200, 400, 1000 or 2000 msec. The contingent negative variation (CNV) was not only measured between S₁ and S₂ (CNV₂), but also before S₁ (CNV₁).The main results were: (1) The CNV₂ amplitude showed significant variation as a function of ISI. It reached its maximum with an ISI of 1000 msec. (2) CNV₁ developed only before the short ISIs (200 and 400 msec). (3) When CNV₁ and CNV₂ were summed the differences in CNV amplitudes and durations between different ISIs became smaller. (4) The peak-to-peak amplitude P₁-N₁ of the potential evoked by S₁ was enhanced with short ISIs. (5) The correlations between mean CNV and median reaction time (RT) were low but significant for ISIs of 400, 1000 and 2000 msec. When, however, the effect of subjects was partialized out these correlations were drastically reduced, whereas the partialization of session and block effects had no noticeable influence on these correlations. (6) The correlations between single RT and single CNV (measured for the ISI of 1000 msec, individually for two subjects) were weak or even completely lacking.The main conclusion was that CNV coincides with preparedness to react to a stimulus in a choice RT-task, but its amplitude at the moment of onset of the imperative stimulus does not reflect, or reflects weakly, the degree of preparedness (as indicated by RTs) at that moment.     

Acoustic determinants of infant preference for motherese speech

Three experiments investigated possible acoustic determinants of the infant listening preference for motherese speech found by Fernald 1985. To test the hypothesis that the intonation of motherese speech was sufficient to elicit this preference, it was necessary to eliminate lexical content and to isolate the three major acoustic correlates of intonation: (1) fundamental frequency (F_o), or pitch; (2) amplitude, correlated with loudness; and (3) duration, related to speech rhythm. Three sets of auditory reinforcers were computer-synthesized, derived from the F_o (Experiment 1), amplitude (Experiment 2), and duration (Experiment 3) characteristics of the infant- and adult-directed natural speech samples used by Fernald 1985. Thus, each of these experiments focused on particular prosodic variables in the absence of segmental variation. Twenty 4-month-old infants were tested in an operant auditory preference procedure in each experiment. Infants showed a significant preference for the F_o-patterns of motherese speech, but not for the amplitude or duration patterns of motherese.     

Timing precision in continuation and synchronization tapping

 Wing and Kristofferson (1973) have shown that temporal precision in self-paced tapping is limited by variability in a central timekeeper and by variability arising in the peripheral motor system. Here we test an extension of the Wing–Kristofferson model to synchronization with periodic external events that was proposed by Vorberg and Wing (1994). In addition to the timekeeper and motor components, a linear phase correction mechanism is assumed which is triggered by the last or the last two synchronization errors. The model is tested in an experiment that contrasts synchronized and self-paced trapping, with response periods ranging from 200–640 ms. The variances of timekeeper and motor delays and the error correction parameters were estimated from the auto-covariance functions of the inter-response intervals in continuation and the asynchronies in synchronization. Plausible estimates for all parameters were obtained when equal motor variance was assumed for synchronization and continuation. Timekeeper variance increased with metronome period, but more steeply during continuation than during synchronization, suggesting that internal timekeeping processes are stabilized by periodic external signals. First-order error correction became more important as the metronome period increased, whereas the contribution of second-order error correction decreased. It is concluded that the extended two-level model accounts well for both synchronization and continuation performance. Received: 16 November 1998 / Accepted: 21 April 1999     

Development of sensorimotor synchronization abilities: Motor and cognitive components

The aim of the present study was to examine both the development of sensorimotor synchronization in children in the age range from 5 to 8 years and the involvement of motor and cognitive capacities. Children performed a spontaneous motor tempo task and a synchronization–continuation task using an external auditory stimulus presented at three different inter-stimulus intervals: 500, 700, and 900 ms. Their motor and cognitive abilities (short-term memory, working memory, and attention) were also assessed with various neuropsychological tests. The results showed some developmental changes in synchronization capacities, with the regularity of tapping and the ability to slow down the tapping rate improving with age. The age-related differences in tapping were nevertheless greater in the continuation phase than in the synchronization phase. In addition, the development of motor capacities explained the age-related changes in performance for the synchronization phase and the continuation phase, although working memory capacities were also involved in the interindividual differences in performance in the continuation phase. The continuation phase is thus more cognitively demanding than the synchronization phase. Consequently, the improvement in sensorimotor synchronization during childhood is related to motor development in the case of synchronization but also to cognitive development with regard to the reproduction and maintenance of the rhythm in memory.     

Mindful Disintegration and the Decomposition of Self in Healthy Populations: Conception and Preliminary Study

The concept and quantification of ‘disintegration’ related to mindfulness were examined, i.e. attentional refinement to microscopic resolution wherein constituents of matter are decomposed into elemental units. Thus, perceptual data are synthesized less coherently. To explore this hypothesis, neural substrates of perceptual disorganization (high-frequency EEG event-related synchronization dynamics—ERD/ERS) and contextual meaning (N400 ERP) were investigated in healthy practitioners before and after a mindfulness retreat. N400 ERP amplitude attenuated, as did gamma-ERD. Shift from beta-ERD to beta-ERS was observed. These findings suggest: (1) mediated gamma-oscillations reflecting disrupted neural binding of visual representation/cohesion, (2) reduced N400 amplitude reflecting diminished extraction of contextual meaning, and (3) modulations in beta-synchrony that may serve to ‘stabilize’ cortical functioning during the transformative disintegrative process related to mindfulness, akin to a process of ‘non-reactivity’ at the cortical level. The latter may provide a candidate neural index for the construct of ‘equanimity’ within the mindfulness purview. An overarching interpretative framework of the results paralleling adaptive versus maladaptive disintegrative experience is further discussed.     

Perception in action: The impact of sensory information on sensorimotor synchronization in musicians and non-musicians

The present study aimed at investigating to what extent sensorimotor synchronization is related to (i) musical specialization, (ii) perceptual discrimination, and (iii) the movement’s trajectory. To this end, musicians with different musical expertise (drummers, professional pianists, amateur pianists, singers, and non-musicians) performed an auditory and visual synchronization and a cross-modal temporal discrimination task. During auditory synchronization drummers performed less variably than amateur pianists, singers and non-musicians. In the cross-modal discrimination task drummers showed superior discrimination abilities which were correlated with synchronization variability as well as with the trajectory. These data suggest that (i) the type of specialized musical instrument affects synchronization abilities and (ii) synchronization accuracy is related to perceptual discrimination abilities as well as to (iii) the movement’s trajectory. Since particularly synchronization variability was affected by musical expertise, the present data imply that the type of instrument improves accuracy of timekeeping mechanisms.     

Regional and inter-regional theta oscillation during episodic novelty processing

Recent event-related potential (ERP) and functional magnetic resonance imaging (fMRI) studies suggest that novelty processing may be involved in processes that recognize the meaning of a novel sound, during which widespread cortical regions including the right prefrontal cortex are engaged. However, it remains unclear how those cortical regions are functionally integrated during novelty processing. Because theta oscillation has been assumed to have a crucial role in memory operations, we examined local and inter-regional neural synchrony of theta band activity during novelty processing. Fifteen right-handed healthy university students participated in this study. Subjects performed an auditory novelty oddball task that consisted of the random sequence of three types of stimuli such as a target (1000 Hz pure tone), novel (familiar environmental sounds such as dog bark, buzz, car crashing sound and so on), and standard sounds (950 Hz pure tone). Event-related spectra perturbation (ERSP) and the phase-locking value (PLV) were measured from human scalp EEG during task. Non-parametric statistical tests were applied to test for significant differences between stimulus novelty and stimulus targets in ERSP and PLV. The novelty P3 showed significant higher amplitude and shorter latency compared with target P3 in frontocentral regions. Overall, theta activity was significantly higher in the novel stimuli compared with the target stimuli. Specifically, the difference in theta power between novel and target stimuli was most significant in the right frontal region. This right frontal theta activity was accompanied by phase synchronization with the left temporal region. Our results imply that theta phase synchronization between right frontal and left temporal regions underlie the retrieval of memory traces for unexpected but familiar sounds from long term memory in addition to working memory retrieval or novelty encoding.     

Getting synchronized with the metronome: Comparisons between phase and period correction

Most studies of synchronization have focused on how an established phase relationship between self-produced events (e.g., finger taps) and the clicks of a metronome is maintained when the metronome is regular or subject to unpredictable perturbations. Here we study how synchronization is initially established, using an experimental paradigm in which the metronome is activated after the subject has executed a series of self-paced finger taps. In Exp. 1, the metronome period was constant and equal to the mean of the self-paced inter-response intervals, whereas the initial phase difference of the metronome from the taps varied across trials. The synchronization error patterns could be predicted by a linear phase correction model. Experiment 2 involved both period and phase correction. The initial phase difference was constant, whereas the metronome period varied across trials. The observed synchronization error patterns suggest that the subjects achieved synchronization either by reacting to the second metronome signal or by aiming at the third metronome signal. The pattern of the residual synchronization errors was consistent with the linear phase correction model. These results support the notion that period and phase correction mechanisms are called for by different task variables and contribute differently to sensorimotor synchronization. Received: 20 November 1996 / Accepted: 20 April 1997     

Effects of feedback from active and passive body parts on spatial and temporal parameters in sensorimotor synchronization

Previous research on sensorimotor synchronization has manipulated the somatosensory information received from the tapping finger to investigate how feedback from an active effector affects temporal coordination. The current study explored the role of feedback from passive body parts in the regulation of spatiotemporal motor control parameters by employing a task that required finger tapping on one’s own skin at anatomical locations of varying tactile sensitivity. A motion capture system recorded participants’ movements as they synchronized with an auditory pacing signal by tapping with the right index finger on either their left index fingertip (Finger/Finger) or forearm (Finger/Forearm). Results indicated that tap timing was more variable, and movement amplitude was larger and more variable, when tapping on the finger than when tapping on the less sensitive forearm. Finger/Finger tapping may be impaired relative to Finger/Forearm tapping due to ambiguity arising through overlap in neural activity associated with tactile feedback from the active and the passive limb in the former. To compensate, the control system may strengthen the assignment of tap-related feedback to the active finger by generating correlated noise in movement kinematics and tap dynamics.     

Early and late SEPs—The later the potential the greater the relevance to personality

Short (N₂₁−P₂₇) and long (N₁₃₀−P₂₀₀) latency somatosensory evoked potentials (SEPs) and personality [Eysenck Personality Questionnaire (EPQ) and a short-form Sensation Seeking scale (SS)] were investigated in 26 young healthy adults. Various modes of analysis were carried out on the SEPs, including peak-to-peak, root mean square, absolute area and perimeter measures, over various time windows. The amount of SEP variance accounted for by personality correlations depended on the mode of analysis. High Psychoticism and high Sensation Seeking (and to some extent high Extraversion) correlated negatively with measures of SEP amplitude, the relationship being stronger for later SEP components.     

Slow cortical and heart rate correlates of discrimination performance

Slow EEG potentials (F_z, C_z, P_z) and heart rate were recorded during the foreperiod of a reaction task, which involved different levels of discrimination difficulty. A simple reaction task was compared with a selective reaction task where either an easy or a difficult discrimination was required. In general, the terminal amplitude of the CNV was not affected by task difficulty. However, a prolonged negative wave was found when the difficulty of the task was not known to the subject in advance but was indicated by S₁. Moreover, the heart-rate deceleration around S₂ was more pronounced the more difficult the discrimination required at S₂.     

Passive avoidance learning produces focal elevation of bursting activity in the chick brain: amnesia abolishes the increase

Presentation of a bright bead to day-old chicks (Gallus domesticus: Ross 1 Chunky Chicks) elicits spontaneous pecking. If the bead is coated with an aversive substance (e.g., methylanthranilate), they will avoid similar beads subsequently; if it is coated with water, they peck avidly on re-presentation. Formation of a memory for this one-trial passive avoidance task is unaffected by subconvulsive transcranial electroshock when applied 10 min after training in 60% of birds, whereas "immediate" post-training electroshock renders 63% of chicks amnesic. Memory formation and retention is associated with a large bilateral enhancement in trained over control chicks (320 and 350% in left and right hemispheres, respectively; p less than 0.001) of a particular spontaneous multi-unit activity firing pattern, that is, short-duration (15-40 ms) bursts of large-amplitude (greater than or equal to 200 microV, 450 microV max p-p), high-frequency (400-450 Hz) spiking in anesthetized chicks. This effect is observed in data lumped from 1-13 h after training and is restricted to the intermediate medial hyperstriatum ventrale. When chicks are rendered amnesic by electroshock immediately following training, there is a complete abolition of this increase in burst firing; in those chicks where this treatment fails to elicit amnesia, the increase in bursting is still observed. In birds in which the shock is delayed and memory formation occurs, the increase in bursting activity is maintained; however, if the delayed shock produces apparent amnesia, then the increase is once again abolished. The electroshock had no effect on bursting per se in untrained chicks. There was no significant difference in tonic spiking between the chicks. A marked increase in the occurrence of bursting epochs in the IMHV of anesthetized chicks following passive avoidance training is therefore closely associated with memory formation, but not with the nonspecific concomitants of the training procedure.