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At least 19 recordsLinked to original sources
PubMed2000

Gamma rhythms and beta rhythms have different synchronization properties.

Experimental and modeling efforts suggest that rhythms in the CA1 region of the hippocampus that are in the beta range (12-29 Hz) have a different dynamical structure than that of gamma (30-70 Hz). We use a simplified model to show that the different rhythms employ different dynamical mechanisms to synchronize, based on different ionic currents. The beta frequency is able to synchronize over long conduction delays (corresponding to signals traveling a significant distance in the brain) that apparently cannot be tolerated by gamma rhythms. The synchronization properties are consistent with data suggesting that gamma rhythms are used for relatively local computations whereas beta rhythms are used for higher level interactions involving more distant structures.

Animals↗
PubMed1992

Fast (beta) rhythms in the hippocampus: a review.

Spontaneous or evoked brain activity in the hippocampus showed a 20-70 Hz beta rhythm under some conditions, typically during behavioral activation and accompanied by a theta rhythm. Beta rhythms are generated locally, perhaps by a recurrent feedback loop involving pyramidal cells and inhibitory interneurons. Modulation of the local circuit and rhythm by cholinergic inputs has also been demonstrated. Under some behavioral states, neural impulses modulated at the beta frequency may transmit preferentially through the trisynaptic circuit in the hippocampus. It is suggested that the beta rhythm may serve to establish transient physiological connections, reflected in coherence at the beta frequency, among neurons in the hippocampus and related structures. Thus, the beta rhythm may play an essential role in hippocampal function.

Animals↗
PubMed1987

Anatomical localization of cortical beta rhythms in cat.

Beta electrocorticographic rhythms (40 Hz) develop during motionless focused attention in two distinct cortical foci in cats. A cytoarchitectonic study was performed to determine the precise location of these foci. Electrode tips recording beta rhythms were found: (i) in motor areas 4 gamma and 6a beta, in a band extending from the postcruciate cortex to the walls of the presylvian sulcus, crossing the frontal pole (anterior beta focus); (ii) in the posterior parietal associative area 5a, along the divisions of the ansate sulcus, extending to the mesial aspect of the hemispheres (posterior beta focus). The two foci are separated by areas 3, 2 and 1, where beta rhythms were never recorded. The fact that both these areas, containing giant pyramidal cells, develop a specific type of activity during immobility may have a functional meaning: area 5 may be involved in the cat as it is in the monkey in the control of motor behaviour.

Animals↗
PubMedDate not supplied

New roles for the gamma rhythm: population tuning and preprocessing for the Beta rhythm.

Gamma (30-80 Hz) and beta (12-30 Hz) oscillations such as those displayed by in vitro hippocampal (CA1) slice preparations and by in vivo neocortical EEGs often occur successively, with a spontaneous transition between them. In the gamma rhythm, pyramidal cells fire together with the interneurons, while in the beta rhythm, pyramidal cells fire on a subset of cycles of the interneurons. It is shown that gamma and beta rhythms have different properties with respect to creation of cell assemblies. In the presence of heterogeneous inputs to the pyramidal cells, the gamma rhythm creates an assembly of firing pyramidal cells from cells whose drive exceeds a threshold. During the gamma to beta transition, a slow outward potassium current is activated, and as a result the cell assembly vanishes. The slow currents make each of the pyramidal cells fire with a beta rhythm, but the field potential of the network still displays a gamma rhythm. Hebbian changes of connections among the pyramidal cells give rise to a beta rhythm, and the cell assemblies are recovered with a temporal separation between cells firing in different cycles. We present experimental evidence showing that such a separation can occur in hippocampal slices.

Animals↗
PubMed2000

Mu and beta rhythm topographies during motor imagery and actual movements.

People can learn to control the 8-12 Hz mu rhythm and/or the 18-25 Hz beta rhythm in the EEG recorded over sensorimotor cortex and use it to control a cursor on a video screen. Subjects often report using motor imagery to control cursor movement, particularly early in training. We compared in untrained subjects the EEG topographies associated with actual hand movement to those associated with imagined hand movement. Sixty-four EEG channels were recorded while each of 33 adults moved left- or right-hand or imagined doing so. Frequency-specific differences between movement or imagery and rest, and between right- and left-hand movement or imagery, were evaluated by scalp topographies of voltage and r spectra, and principal component analysis. Both movement and imagery were associated with mu and beta rhythm desynchronization. The mu topographies showed bilateral foci of desynchronization over sensorimotor cortices, while the beta topographies showed peak desynchronization over the vertex. Both mu and beta rhythm left/right differences showed bilateral central foci that were stronger on the right side. The independence of mu and beta rhythms was demonstrated by differences for movement and imagery for the subjects as a group and by principal components analysis. The results indicated that the effects of imagery were not simply an attenuated version of the effects of movement. They supply evidence that motor imagery could play an important role in EEG-based communication, and suggest that mu and beta rhythms might provide independent control signals.

Adolescent↗
PubMed1983

[Localized frontoparietal beta rhythms and focused attention in animals].

In normal cats and monkeys, fronto-parietal beta rhythms (averages: 36 and 18 c/sec, respectively) were considered as a sign of focused attention, since they appeared during several different situations having in common that the subject's attention was drawn by a signal or an object of the environment. These regular rhythmic activities, often with a high amplitude, are localized within two small cortical foci. At least one set of beta rhythms corresponds to the end station of a thalamocortical system originating in the posterior group (POm), and are controlled by a dopaminergic system the somas of which are situated in the ventral mesencephalic tegmentum (area A10). Eight percent of the VMT cells, studied with micropipettes in normal awake cats, suddenly increased their spontaneous activity 1 sec before the beginning of the rhythmic volleys. Considering the analogy between these rhythms and the human frontal beta rhythms, it is suggested that these data may contribute to the study of attention in man, whether in a healthy state or suffering from mental disease.

Animals↗
PubMed1997

Effects of handedness on movement-related changes of central beta rhythms.

The effects of handedness on the movement-related changes in beta rhythms (14-30 Hz) in the left and right perirolandic area were analyzed in 12 right-handed and 11 left-handed subjects. The motor task consisted of unilateral brisk or slow self-paced extension of the right or left index finger. The handedness effects were as follows. First, in both handedness groups, the premovement desynchronization of beta rhythms at both hemispheres was greatest before slow movement of the "nondominant" finger, especially at electrodes presumably overlying the MI areas. Second, the lefthanded group showed less desynchronization in both hemispheres during execution of a slow movement than the righthanded group. Third, the postmovement beta synchronization showed a contralateral preponderance which was greater after movements of the nondominant than the "dominant" finger in the righthanded group and was equal for both fingers in the lefthanded group. The results suggest that handedness effects on movement-related changes in central beta rhythms are coupled to movements of the nondominant finger and that their manifestation differs in the pre- and postmovement periods.

Adult↗
PubMed1994

Relationship between posterior thalamic nucleus unit activity and parietal cortical rhythms (beta) in the waking cat.

Cat behavioural states of attentive fixation on a target are associated with episodes of electrocortical rhythms at 40 Hz ("beta rhythms") in the parietal cortex. Previous field potential studies indicate that the nucleus posterior pars medialis of the thalamus displays this particular rhythmic activity. We investigated single units of the nucleus posterior pars medialis and its surrounding nuclei to assess their participation in the cortical beta rhythms. Only a small proportion of thalamic cells underwent changes in their firing pattern during beta episodes. "Beta-related cells" were localized in the nucleus posterior pars medialis or its immediate vicinity; no such beta-related cells were found in other regions of the lateral thalamus. Some beta-related cells showed a one-spike to one-wave relationship ("homorhythmicity"), while others displayed a prolonged decrease or a suppression of their firing throughout each beta episode ("pause cells"). For comparison, neurons in the same thalamic area were also recorded during sleep episodes with slow waves and spindles: there was no correlation between spindles and cell firing. Thus, the nucleus posterior pars medialis thalamic nucleus contains cells whose firing is correlated with the beta rhythms. No such correlation was found with sleep spindles.

Animals↗
PubMed1995

Desynchronization and recovery of beta rhythms during brisk and slow self-paced finger movements in man.

Event-related desynchronization (ERD) and recovery of EEG beta rhythms (15-26 Hz) were studied during slow and brisk self-paced index finger extension and flexion. beta rhythms started to recover earlier in brisk movements. Brisk movements showed no correlation between duration of EMG burst in the extensor muscle and the latency of recovery whereas slow movements did. In contrast to beta-ERD which was widespread, the recovery and rebound of beta rhythms occurred in a circumscribed focus close to the hand MI area.

Adult↗
PubMed1996

Event-related desynchronisation of central beta-rhythms during brisk and slow self-paced finger movements of dominant and nondominant hand.

Changes in central beta-rhythms (14-29 Hz) during movement were investigated in 12 right-handed subjects by quantifying event-related desynchronisation (ERD). EEG was recorded from 24 closely spaced electrodes overlaying the left and right sensorimotor hand area. The subjects performed approximately 80 brisk (movement time < 0.21 s) and 80 slow (movement time 1.3-2.1 s) self-paced extensions of their left or right index finger. Beta-band power attenuation in the preparatory period (2.0-0.5 s before movement onset) was larger in the contralateral hemisphere in both types of movement and similar for both fingers. In the 0.4-s period before the onset of extensor muscle contraction, right-finger movements only showed a significant contralateral preponderance of beta-ERD. During movement an anterior ERD predominance in the right sensorimotor hand area and a widespread ERD in the left sensorimotor area was found for both fingers. The recovery and rebound of beta-rhythms showed contralateral preponderance which was expressed more in the right hemisphere, especially after left-finger movements. The results suggest that the dynamics of premovement desynchronisation and postmovement synchronisation of central beta-rhythms is related to hand dominance.

Adult↗
PubMed1994

Visualization of sensorimotor areas involved in preparation for hand movement based on classification of mu and central beta rhythms in single EEG trials in man.

It is well known that mu and central beta rhythms start to desynchronize > 1 s before active hand or finger movement. To investigate whether the same cortical areas are involved in desynchronization of mu and central beta rhythms, 56-channel EEG recordings were made during right- and left-finger flexions in three normal subjects. The event-related desynchronization (ERD) was quantified in single EEG trials and classified by the Distinction Sensitive Learning Vector Quantization (DSLVQ) algorithm. This DSLVQ selects the most relevant features (electrode positions) for discrimination between the preparatory state for left- and right-finger movements. It was found that the most important electrode positions were close to the primary hand area. However, in all three subjects the focus of the central beta ERD was slightly anterior to the focus of mu desynchronization. This can be interpreted that different neural networks are involved in the generation of mu and central beta rhythms.

Electroencephalography↗
PubMed1982

Ventral mesencephalic tegmentum (VMT) controls electrocortical beta rhythms and associated attentive behaviour in the cat.

When a cat is immobile, very alert and displaying behaviour suggesting focused attention toward a target in its environment, beta rhythms (ca. 40 Hz) develop in the fronto-parietal cortical areas. After bilateral electrolytic lesions of the ventral mesencephalic tegmentum (VMT), these beta rhythms are suppressed (while other cortical activities, with other behavioural correlates, persist), and at the same time, attentive immobility is no longer observed: the same experimental situation as in the control now elicits locomotor hyperactivity. Arguments are produced, favouring the hypothesis that both behavioural immobility and the accompanying thalamocortical beta rhythms are controlled through one of the dopaminergic system that originate from the VMT and are distinct from the nigrostriatal one.

Animals↗
PubMed1992

Nucleus reticularis thalami participates in sleep spindles, not in beta rhythms concomitant with attention in cat.

In the awake cat, characteristic electrocortical synchronized oscillations (beta rhythms) can develop on the parietal cortex in specific behavioural situations such as during attentive fixation of a target. These activities differ from other synchronized rhythms which accompany slow sleep ("spindles") and are more widespread. It is shown here through single unit recording from the thalamic nucleus reticularis (RET), that the latter structure participates in spindles (as already postulated by other authors), but not in the beta rhythms which seem to depend on a more restricted thalamic focus in the posterior thalamic nucleus. These data thus support the idea that RET plays a role in slow-wave sleep but not in the cognitive operations involved in focussing attention.

Animals↗
PubMed2005

On the human sensorimotor-cortex beta rhythm: sources and modeling.

Cortical oscillations in the beta band (13-35 Hz) are known to be modulated by the GABAergic agonist benzodiazepine. To investigate the mechanisms generating the approximately 20-Hz oscillations in the human cortex, we administered benzodiazepines to healthy adults and monitored cortical oscillatory activity by means of magnetoencephalography. Benzodiazepine increased the power and decreased the frequency of beta oscillations over rolandic areas. Minimum current estimates indicated the effect to take place around the hand area of the primary sensorimotor cortex. Given that previous research has identified sources of the beta rhythm in the motor cortex, our results suggest that these same motor-cortex beta sources are modulated by benzodiazepine. To explore the mechanisms underlying the increase in beta power with GABAergic inhibition, we simulated a conductance-based neuronal network comprising excitatory and inhibitory neurons. The model accounts for the increase in the beta power, the widening of the spectral peak, and the slowing down of the rhythms with benzodiazepines, implemented as an increase in GABAergic conductance. We found that an increase in IPSCs onto inhibitory neurons was more important for generating neuronal synchronization in the beta band than an increase in IPSCs onto excitatory pyramidal cells.

Adult↗
PubMed1981

Central beta rhythm during sensorimotor activities in man.

Blocking or desynchronization of the central beta rhythm prior to and parallel to voluntary movement was found in 31 of 33 normal subjects investigated. The beta blocking was short lasting (1-3 sec), very often accompanied by blocking of the mu rhythm and localized in the central region. Phasic beta desynchronization was also observed after somatosensory stimulation. The beta rhythm showed a bilateral symmetrical blocking pattern with unilateral movement or stimulation. Patients with unilateral cerebral ischaemia showed an asymmetric blocking response and therefore demonstrated a high degree of hemispheric independence of the rhythmic generating systems. Central beta desynchronization is, therefore, a normal physiological phenomenon caused by activation processes of the sensorimotor cortex and detectable on the scalp very easily with closely spaced electrodes.

Beta Rhythm↗
PubMed2005

Intra-operative STN DBS attenuates the prominent beta rhythm in the STN in Parkinson's disease.

Power spectra from local field potentials (LFPs) recorded post-operatively from the deep brain stimulation (DBS) macroelectrode show prominence of the beta rhythm (11-30 Hz) in untreated Parkinson's disease (PD). Dopaminergic medication and movement attenuate this beta band in PD. In this pilot study of six sides in four patients, we recorded LFPs from the DBS electrode in untreated PD patients in the operating room. In all cases, there was a peak in the time-frequency spectrogram in the beta frequency range when the patients were at rest, which was associated with attenuation in the same range with movement. The actual frequency range and the strength of the beta peak varied among cases. In two patients, intra-operative constraints permitted recording of LFPs at rest, before and immediately after subthalamic nucleus (STN) DBS. In both patients we documented that STN DBS caused a significant attenuation in power in the beta band at rest that persisted for 15-25 s after DBS had been turned off (P < 0.01). From one case, our data suggest that the beta rhythm attenuation was most prominent within the STN itself. This study shows for the first time that STN DBS attenuates the power in the prominent beta band recorded in the STN of patients with PD. These pilot findings raise the interesting possibility of using this biomarker for closed loop DBS or neuromodulation.

Beta Rhythm↗