Presence Of Theta Rhythm Research Articles

Respiration and rapid eye movement (REM) sleep substructure: short versus long episodes.

Rapid eye movement (REM) sleep in rodents is defined by the presence of theta rhythm in the absence of movement. The amplitude and frequency of theta oscillations have been used to distinguish between tonic and phasic REM sleep. However, tonic REM sleep has not been further subdivided, although characteristics of network oscillations such as cross-frequency coupling between theta and gamma vary within this sub-state. Recently, it has been shown that theta-gamma coupling depends on an optimal breathing rate of ~5 Hz. The frequency of breathing varies strongly throughout REM sleep, and the duration of single REM sleep episodes ranges from several seconds to minutes, whereby short episodes predominate. Here we studied the relation between breathing frequency, accelerometer activity, and the length of REM sleep periods. We found that small movements detected with three-dimensional accelerometry positively correlate with breathing rate. Interestingly, breathing is slow in short REM sleep episodes, while faster respiration regimes exclusively occur after a certain delay in longer REM sleep episodes. Thus, merging REM sleep episodes of different lengths will result in a predominance of slow respiration due to the higher occurrence of short REM sleep periods. Moreover, our results reveal that not only do phasic REM sleep epochs predominantly occur during long REM sleep episodes, but that the long episodes also have faster theta and higher gamma activity. These observations suggest that REM sleep can be further divided from a physiological point of view depending on its duration. Higher levels of arousal during REM sleep, indicated by higher breathing rates, can only be captured in long REM sleep episodes.

The Immediate Early GeneArc/Arg3.1: Regulation, Mechanisms, and Function

In a manner unique among activity-regulated immediate early genes (IEGs), mRNA encoded by Arc (also known as Arg3.1) undergoes rapid transport to dendrites and local synaptic translation. Despite this intrinsic appeal, relatively little is known about the neuronal and behavioral functions of Arc or its molecular mechanisms of action. Here, we attempt to distill recent advances on Arc spanning its transcriptional and translational regulation, the functions of the Arc protein in multiple forms of neuronal plasticity [long-term potentiation (LTP), long-term depression (LTD), and homeostatic plasticity], and its broader role in neural networks of behaving animals. Worley and colleagues have shown that Arc interacts with endophilin and dynamin, creating a postsynaptic trafficking endosome that selectively modifies the expression of AMPA-type glutamate receptors at the excitatory synapses. Both LTD and homeostatic plasticity in the hippocampus are critically dependent on Arc-mediated endocytosis of AMPA receptors. LTD evoked by activation of metabotropic glutamate receptors depends on rapid Arc translation controlled by elongation factor 2. Bramham and colleagues have shown that sustained translation of newly induced Arc mRNA is necessary for cofilin phosphorylation and stable expansion of the F-actin cytoskeleton underlying LTP consolidation in the dentate gyrus of live rats. In addition to regulating F-actin, Arc synthesis maintains the activity of key translation factors during LTP consolidation. This process of Arc-dependent consolidation is activated by the secretory neurotrophin, BDNF. Moore and colleagues have shown that Arc mRNA is a natural target for nonsense-mediated mRNA decay (NMD) by virtue of its two conserved 3'-UTR introns. NMD and other related translation-dependent mRNA decay mechanisms may serve as critical brakes on protein expression that contribute to the fine spatial-temporal control of Arc synthesis. In studies in behaving rats, Guzowski and colleagues have shown that location-specific firing of CA3 and CA1 hippocampal neurons in the presence of theta rhythm provides the necessary stimuli for activation of Arc transcription. The impact of Arc transcription in memory processes may depend on the specific context of coexpressed IEGs, in addition to posttranscriptional regulation of Arc by neuromodulatory inputs from the amygdala and other brain regions. In sum, Arc is emerging as a versatile, finely tuned system capable of coupling changes in neuronal activity patterns to diverse forms of synaptic plasticity, thereby optimizing information storage in active networks.

Rhythmic firing of medial septum non-cholinergic neurons.

The presence of theta rhythm (5-10 Hz) in the hippocampus has been shown to enable long-term potentiation, a synaptic mechanism which has been proposed to underlie learning and memory. Medial septum cholinergic and GABAergic neurons that project to the hippocampus have been hypothesized to play conjointly a major role in the genesis of this rhythm. Building upon previous studies that have established the electrophysiological criteria for distinguishing cholinergic and non-cholinergic neurons in this area, it is demonstrated here that medial septum non-cholinergic neurons, putatively GABAergic, have the ability to discharge in rhythmic clusters of action potentials occurring at frequencies ranging from 1 to 8 Hz. Within the clusters, the firing frequency of action potentials varied between 13 and 57 Hz in a voltage-dependent manner. In addition, small voltage-dependent subthreshold membrane potential oscillations (16-54 Hz) were observed between clusters. Both subthreshold oscillations and clusters were eliminated by tetrodotoxin at 1 microM. These results indicate that non-cholinergic medial septum neurons could convey to the hippocampus not only theta but also higher frequency rhythmicity in the beta-gamma range (20-60 Hz).

Neuronal sources of theta rhythm in the entorhinal cortex of the rat. I. Laminar distribution of theta field potentials.

The laminar distribution of theta (theta) field potentials in the entorhinal cortex (EC) was investigated in paralysed and locally anesthetized rats injected with physostigmine in order to induce theta rhythm. Electrode penetrations through the medial, intermediate and lateral subdivisions of the EC showed in all cases: 1. the presence of theta rhythm from layer VI to layer III approximately in phase with CA1 theta rhythm; 2. an amplitude minimum between the outer third of layer III and the inner half of layer I; and 3. a phase-reversed theta rhythm in layers II-I with an amplitude maximum in the outer half of layer I. Results indicate the existence of neuronal sources of theta rhythm in the EC.

Hippocampal theta rhythm used in predicting feline behavior

Abstract Cats were trained to discriminate between two auditory signals, responding to one by running down a short alleyway to food, and to the other by remaining in the start box. After training, the telemetered hippocampal electroencephalogram was recorded during the conditioned signals for 100 trials in each animal. The presence of theta rhythm (4–7 c/s) was taken to indicate that the animal would run. It was possible to predict the animal's subsequent behavior with a high degree of accuracy.

Statistical study of the frequency and reactivity patterns of the electro-encephalograms of aged subjects

Previous studies have brought us to consider the variations in frequency of the basic alpha rhythm of the electroencephalograms, as an important and significant factor. Regarding the problem of the aging processus, we have looked for an eventual relationship between this fact and the variations in question. For this, we isolated a group of tracings showing no pathological pattern, or belonging to a group of control with no consumption of neuroleptics and able to be part of a “normal” existence. These 879 selected tracings have shown the alpha rhythm in all cases, and in 262 subjects its association with theta rhythm. They may be divided into 5 groups by decades: 1 test-group from 30 to 39 years (349 tracings). 1 group of comparison from 50 to 59 years (270 tracings). 1 group of comparison from 60 to 69 years (166 tracings). 1 group of comparison from 70 to 79 years (72 tracings). 1 group of comparison from 80 to 89 years (22 tracings). Even if these groups diminish in number with advancing age, as in all populations studied under this aspect, they remain sufficient in number to be compared under histographic form, grouping the different frequencies of alpha rhythm or according to their average frequencies. The first observation issued from this comparison is the decrease of alpha frequency with age. Among the four groups, the first group only can be compared to the test-group from 30 to 39 years of age. From 60 …. years of age, we see a profile clearly diverted to the left, whereas the averages diminish. The presence of theta rhythm in a tracing favors the reduction in the frequency of alpha rhythm as it is seen if we select in each group, the tracings composed of alpha rhythm (pure alpha rhythm) and those composed of both (alpha + theta). In what concerns reactivity, we have observed that during the aging processus: — the blocking is less and less adequate; — hyperventilation is more and more active; — theta rhythm increases; — the photic stimulation follows less the cerebral rhythm but its action increases the “irritative pattern” or in the appearance of theta rhythm. Moreover, the morphology of the tracing changes and the “choppy” rhythms become more and more abundant. In conclusion: The E.E.G. evolves in one way towards a decrease of the alpha frequency, which is considered as a minor but constant indication of “cerebral distress” and in another way, towards a pattern of reactivity showing, either a decrease of physiological responses, or an increase in pathological elements (vascular types, in particular).