Gamma rhythms and beta rhythms have different synchronization properties

Abstract

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. Rhythms in the gamma range (30-80 Hz) and the beta range (12-30 Hz) are found in many parts of the nervous system and are associated with attention, perception, and cognition (1-3). It has been noted in electroencephalogram (EEG) signals that rhythms of different frequencies are found simultaneously (4). Beta oscillations are readily observable immediately after evoked gamma oscillations in sensory evoked potential recordings (5). This beta activity has been correlated with the long-range synchronous activity of neocortical regions during visuomotor reflex activation (6).This paper concerns the correlation between the frequency band of coherent oscillations and conduction delays between the sites participating in the coherent rhythm. It has been noted (7) in human EEG subjects that gamma rhythms are prevalent in local visual response synchronization, but more distant coherence occurring during multimodal integration between parietal and temporal cortices uses rhythms at frequencies of 12-20Hz (the so-called beta 1 range).We shall use data from the CA1 region of the hippocampus (8-10) as a paradigm to address the questions of how long-distance synchrony is achieved and why there is a correlation between oscillation frequency and the temporal distances between participating sites. The data available from the rat hippocampus slice preparation give clues about details of dynamics that are important to the synchronization process.The work builds on earlier work (11-12) describing and analyzing the role of doublet spikes in interneurons in producing synchrony when there are significant conduction delays. Earlier work (13) using rate models showed, via simulations, that longer conduction delays could be tolerated and still produce synchrony if the carrier rhythm had lower frequencies. However, a rate model is not consistent with the situation in which excitatory cells fire at most one spike per cycle, and with high precision in phase. An alternative solution was suggested by data and large-scale models of the gamma rhythm in the hippocampus (8, 9). In both data and models, the ability to synchronize happened in those parameter regimes in which interneurons produced a spike doublet in many of the cycles. This mechanism was analyzed by Ermentrout and Kopell (11), wh...

EEG synchrony during a perceptual-cognitive task: Widespread phase synchrony at all frequencies

“…Our present finding of intermittent long-range synchrony at all passbands from theta to epsilon (aka high gamma) conflicts with the suggestion (Kopell et al, 2000;Von Stein and Sarnthein, 2000;Von Rullen and Koch, 2003) that long-range synchrony occurs only in low frequency bands (Arieli et al, 1995), while gamma oscillations are synchronous only in local networks or at most between a few cortical areas (Eckhorn, 1994;Steriade et al, 1996;Engel et al, 1991b;Roelfsema et al, 1997). In fact the suggestion that theta/alpha or theta/apha/beta synchrony is global while gamma or beta/gamma-synchrony is local has already been negated by numerous reports of long-range gamma synchrony coinciding with various conscious experiences (Haig et al, 2000;Bhattacharya et al, 2001;Gruber et al, 2001;Lutz et al, 2002;Summerfield and Mangels, 2005).…”

Altered cortical beta‐band oscillations reflect motor system degeneration in amyotrophic lateral sclerosis

“…Physiological beta synchrony is promoted in expectation of impending perturbation to a desired posture [Androulidakis et al, 2007] but is also sensitive to the uncertainty of motor outcome estimation [Tan et al, 2016]. Beta oscillations may also contribute to long‐range communication across cortical regions [Engel and Fries, 2010; Kopell et al, 2000] and can facilitate modulation of selective attention in support of action selection [Grent‐'t‐Jong et al, 2013, 2014; Tzagarakis et al, 2010], beyond simple correlation with reaction times [van Ede et al, 2012]. The abnormalities in this characteristic motor system rhythm displayed by ALS patients (amplified beta desychronization and attenuated beta rebound) may reflect or even contribute to an excitotoxic degeneration of neural microcircuitry, particularly given the apparent correlation with rate of disease progression.…”

Spikes, synchrony, and attentive learning by laminar thalamocortical circuits

“…Kopell et al (2000) proposed that γ and β oscillations might subserve different functional roles. Their simulations showed that β oscillations are more robust in synchronizing areas separated by larger transmission delays, whereas γ oscillations tend to be dispersed when significant delays are interposed.…”