Theta Ratio Research Articles

Increased cerebral activity suppresses baroreflex control of heart rate in freely moving mice

We assessed whether increased cerebral activity suppressed baroreflex control of heart rate (HR) and, if so, whether this occurred prior to the onset of locomotion in daily activity of mice. We measured mean arterial pressure (MAP, arterial catheter), cerebral blood flow in the motor cortex (CBF, laser-Doppler flowmetry), and electroencephalogram in free-moving mice (n = 8) during 12 daytime hours. The contribution of baroreflex control of HR to MAP regulation was determined during a total resting period for approximately 8 h from the cross-correlation function (R(t)) between spontaneous changes in HR (HR) and MAP (MAP) every 4 s and the sensitivity was determined from HR/MAP where R(t) was significant (P < 0.05). The power density ratio of theta to delta wave band in electroencephalogram (theta/delta), determined every 4 s as an index of cerebral activity, was positively correlated with CBF during 73 +/- 3% of the total resting period (P < 0.05) and with R(t) during 59 +/- 2% (P < 0.05). When each measurement during the resting period was divided into seven bins according to the level of theta/delta, CBF was 91 +/- 2% in the lowest bin and 118 +/- 3% in the highest bin (P < 0.001), R(t) was 0.69 +/- 0.06 and 0.27 +/- 0.04 (P < 0.001) and HR/MAP (beats min(1) mmHg(1)) was 12.4 +/- 0.9 and 7.5 +/- 0.9 (P < 0.001), respectively, with significant correlations with theta/delta (all P < 0.002). Moreover, mice started to move in approximately 30 sec after the sequential increases of theta/delta and R(t), mice started to move at 5 times higher probability than after a given time, followed by a rapid increase in MAP by approximately 10 mmHg. These results suggest that increased cerebral activity suppresses baroreflex control of HR and this might be related to the start of voluntary locomotion with a rapid increase in MAP.

Hippocampo–cerebellar theta band phase synchrony in rabbits

Hippocampal functioning, in the form of theta band oscillation, has been shown to modulate and predict cerebellar learning of which rabbit eyeblink conditioning is perhaps the most well-known example. The contribution of hippocampal neural activity to cerebellar learning is only possible if there is a functional connection between the two structures. Here, in the context of trace eyeblink conditioning, we show (1) that, in addition to the hippocampus, prominent theta oscillation also occurs in the cerebellum, and (2) that cerebellar theta oscillation is synchronized with that in the hippocampus. Further, the degree of phase synchrony (PS) increased both as a response to the conditioning stimuli and as a function of the relative power of hippocampal theta oscillation. However, the degree of PS did not change as a function of either training or learning nor did it predict learning rate as the hippocampal theta ratio did. Nevertheless, theta band synchronization might reflect the formation of transient neural assemblies between the hippocampus and the cerebellum. These findings help us understand how hippocampal function can affect eyeblink conditioning, during which the critical plasticity occurs in the cerebellum. Future studies should examine cerebellar unit activity in relation to hippocampal theta oscillations in order to discover the detailed mechanisms of theta-paced neural activity.

Hippocampal theta activity is selectively associated with contingency detection but not discrimination in rabbit discrimination‐reversal eyeblink conditioning

The relative power of the hippocampal theta-band ( approximately 6 Hz) activity (theta ratio) is thought to reflect a distinct neural state and has been shown to affect learning rate in classical eyeblink conditioning in rabbits. We sought to determine if the theta ratio is mostly related to the detection of the contingency between the stimuli used in conditioning or also to the learning of more complex inhibitory associations when a highly demanding delay discrimination-reversal eyeblink conditioning paradigm is used. A high hippocampal theta ratio was not only associated with a fast increase in conditioned responding in general but also correlated with slow emergence of discriminative responding due to sustained responding to the conditioned stimulus not paired with an unconditioned stimulus. The results indicate that the neural state reflected by the hippocampal theta ratio is specifically linked to forming associations between stimuli rather than to the learning of inhibitory associations needed for successful discrimination. This is in line with the view that the hippocampus is responsible for contingency detection in the early phase of learning in eyeblink conditioning.

Hippocampal theta-band activity and trace eyeblink conditioning in rabbits.

The authors examined the relationship between hippocampal theta activity and trace eyeblink conditioning. Hippocampal electrophysiological local field potentials were recorded before, during, and after conditioning or explicitly unpaired training sessions in adult male New Zealand White rabbits. As expected, a high relative power of theta activity (theta ratio) in the hippocampus predicted faster acquisition of the conditioned response during trace conditioning but, contrary to previous results obtained using the delay paradigm, only in the initial stage of learning. The presentation of the conditioned stimulus overall elicited an increase in the hippocampal theta ratio. The theta ratio decreased in the unpaired group as a function of training, remained high throughout conditioning in the fast learners, and rapidly increased in the slow learners initially showing a low theta ratio. Our results indicate a reciprocal connection between the hippocampal oscillatory activity and associative learning. The hippocampal theta ratio seems to reflect changes and differences in the subjects' alertness and responsiveness to external stimuli, which affect the rate of learning and are, in turn, affected by both conditioning and unpaired training.

A theory of alpha/theta neurofeedback, creative performance enhancement, long distance functional connectivity and psychological integration

Professionally significant enhancement of music and dance performance and mood has followed training with an EEG-neurofeedback protocol which increases the ratio of theta to alpha waves using auditory feedback with eyes closed. While originally the protocol was designed to induce hypnogogia, a state historically associated with creativity, the outcome was psychological integration, while subsequent applications focusing on raising the theta-alpha ratio, reduced depression and anxiety in alcoholism and resolved post traumatic stress syndrome (PTSD). In optimal performance studies we confirmed associations with creativity in musical performance, but effects also included technique and communication. We extended efficacy to dance and social anxiety. Diversity of outcome has a counterpart in wide ranging associations between theta oscillations and behaviour in cognitive and affective neuroscience: in animals with sensory-motor activity in exploration, effort, working memory, learning, retention and REM sleep; in man with meditative concentration, reduced anxiety and sympathetic autonomic activation, as well as task demands in virtual spatial navigation, focussed and sustained attention, working and recognition memory, and having implications for synaptic plasticity and long term potentiation. Neuroanatomical circuitry involves the ascending mescencephalic-cortical arousal system, and limbic circuits subserving cognitive as well as affective/motivational functions. Working memory and meditative bliss, representing cognitive and affective domains, respectively, involve coupling between frontal and posterior cortices, exemplify a role for theta and alpha waves in mediating the interaction between distal and widely distributed connections. It is posited that this mediation in part underpins the integrational attributes of alpha-theta training in optimal performance and psychotherapy, creative associations in hypnogogia, and enhancement of technical, communication and artistic domains of performance in the arts.

Hippocampal theta (3–8 Hz) activity during classical eyeblink conditioning in rabbits

In 1978, Berry and Thompson showed that the amount of theta (3–8Hz) activity in the spontaneous hippocampal EEG predicted learning rate in subsequent eyeblink conditioning in rabbits. More recently, the absence of theta activity during the training trial has been shown to have a detrimental effect on learning rate. Here, we aimed to further explore the relationship between theta activity and classical eyeblink conditioning by determining how the relative power of hippocampal theta activity [theta/(theta+delta) ratio] changes during both unpaired control and paired training phases. We found that animals with a higher hippocampal theta ratio immediately before conditioning learned faster and also that in these animals the theta ratio was higher throughout both experimental phases. In fact, while the hippocampal theta ratio remained stable in the fast learners as a function of training, it decreased in the slow learners already during unpaired training. In addition, the presence of hippocampal theta activity enhanced the hippocampal model of the conditioned response (CR) and seemed to be beneficial for CR performance in terms of peak latency during conditioning, but did not have any effect when the animals showed asymptotic learning. Together with earlier findings, these results imply that the behavioral state in which hippocampal theta activity is absent is detrimental for learning, and that the behavioral state in which hippocampal theta activity dominates is beneficial for learning, at least before a well-learned state is achieved.

Lack of the metabotropic glutamate receptor subtype 7 selectively modulates Theta rhythm and working memory

Metabotropic glutamate receptors (mGluRs) are known to play a role in synaptic plasticity and learning. We have previously shown that mGluR7 deletion in mice produces a selective working memory (WM) impairment, while other types of memory such as reference memory remain unaffected. Since WM has been associated with Theta activity (6-12 Hz) in EEGs, and since EEG abnormalities have been observed in these mice before, we studied the effect of mGluR7 gene ablation on EEG activity in the hippocampus, in particular in the Theta range, during performance of a WM task. In an eight-arm maze with four arms baited, mGluR7 knock-out (KO) and wild-type mice committed the same number of reference memory errors, whereas KOs committed more WM errors. While performing the task, KO mice showed substantially higher Theta amplitudes, and the ratio of Theta to overall EEG power was much increased. No change was seen in the Delta (0-5 Hz), or Gamma (30-40 Hz) EEG bands compared with controls. When recording EEGs during periods of rest in the home cages, no difference was seen between groups. These findings suggest that mGluR7 is important for modulation and control of Theta activity. Since only WM was affected, and only the Theta range of EEG activity was altered, these results show a correlation between Theta rhythm and WM performance, and therefore support the concept that Theta activity in the hippocampus is involved in WM storage.

Limits for the Central Production ofΘ+andΞ--Pentaquarks in 920-GeV pA Collisions

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).

Light-front approach for heavy pentaquark transitions

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively.

A promoter variant of the heme oxygenase-1 gene may reduce the incidence of ischemic heart disease in Japanese

Heme oxygenase-1 (HO-1) has been suggested to have antiatherogenic properties. This study was designed to examine the relationship between the HO-1 gene ( HMOX1) and ischemic heart disease. The study population consisted of 1972 control subjects and 597 subjects with ischemic heart disease (myocardial infarction (MI) n=393, HMOX1 n=204 ). The control subjects were consecutively selected from the Suita study, an epidemiological cohort representing the general population in Japan. Patients with ischemic heart disease were recruited from the outpatient clinic of the National Cardiovascular Center (NCVC). We sequenced HMOX1 and found a T(− 413) A polymorphism in the promoter region. Multiple logistic analyses indicated that the T(− 413) A ( TA+ TT/ AA) polymorphism, sex, smoking habit, DM and BMI affected the occurrence of ischemic heart disease. The odds ratios of the TA+ TT allele for MI and AP were 1.42 ( P=0.0468, 95% confidence interval: 0.01–0.35) and 1.86 ( P=0.0096, 95% confidence interval: 0.08–0.55), respectively. Luciferase reporter assay indicated that the A allele promoter had significantly higher activity than the T allele promoter. The AA genotype of HMOX1 reduced the incidence of ischemic heart disease, possibly due to the high expression level of HMOX1.

Waking quantitative electroencephalogram and auditory event-related potentials following experimentally induced sleep fragmentation.

Experimental sleep fragmentation involves inducing arousals by administering intrusive auditory stimuli throughout the night. It is intended to model the frequent and periodic disruption experienced in common sleep disorders. Sleep fragmentation leads to daytime sleepiness, although evidence of performance impairment has been inconsistent. The purpose of this study was to investigate brain physiology associated with this level of sleep disruption. Specifically, quantitative analysis of electroencephalography was carried out, and auditory event-related potentials were recorded during daytime performance assessment following sleep fragmentation in good sleepers. Participants spent 4 consecutive 24-hour periods in the laboratory. On nights 2 and 3, sleep was fragmented using auditory stimuli that were delivered with increasing intensity until an arousal was noted. This design aimed to investigate the cumulative effects of sleep fragmentation on daytime functioning. Data were collected in a sleep research laboratory during a 96-hour protocol. Eight healthy adults (mean age = 33.25) with no sleep complaints. During the day, participants performed a 40-minute computerized test battery at 2-hour intervals (9:00 am -7:00 pm). The battery was presented in a fixed order and included measures of mood, sleepiness, reaction time, and serial addition or subtraction. Results indicated that subjective sleepiness and mood were impaired following sleep-fragmentation nights, compared to both baseline and recovery conditions. No performance deficits were apparent. The alpha:theta ratio, reflecting relative slowing of the electroencephalogram, was dramatically reduced following the second night of sleep fragmentation. Reductions in N1 amplitude of the event-related potentials indicated that attention was impaired with respect to early encoding processes following sleep fragmentation. Electroencephalographic and event-related potentials data illustrate impairment in information-processing capabilities associated with reduced arousal elicited by experimental sleep fragmentation. This subtle degree of sleep disruption, where total sleep time is not reduced, leads to sustained impairment in alertness and attention.

Microstructural and electrical characteristics of reactively sputtered Ta-N thin films

Ta–N thin films were prepared by RF magnetron sputtering a Ta target in an Ar+N 2 atmosphere, with the nitrogen gas flow ratio varying from 0 to 15%. The resistivity and deposition rate were measured and the microstructure of the films was characterized using glancing-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The resistivity of the Ta–N films increases, while the deposition rate decreases, with increasing N 2 flow. The N/Ta ratio of the Ta–N films sputtered with 1% of N 2 is 1:2, while those of the films sputtered with 2.5–15% of N 2 are all approximately 1. X-Ray diffraction reveals that the zero-N 2 film shows a b.c.c. Ta structure, and the films with 1, 2.5–10 and 15% of N 2 are amorphous, f.c.c. TaN and amorphous, respectively. However, electron diffraction shows that, in addition to the amorphous phase, the Ta–N film sputtered with 1% of N 2 also contains nanocrystalline β-Ta and Ta 2N phases. X-Ray photoelectron spectroscopy indicates that the 1% N 2 Ta–N film shows an intermediate bonding state between metallic Ta and TaN, while the films with 2.5–15% N 2 exhibit TaN bonding. Correlation between the film resistivity and the microstructral characteristics of sputtered Ta–N films is discussed.

Searching for hidden information with Gabor Transform in generalized tonic-clonic seizures

The analysis of generalized tonic clonic seizures is usually difficult with scalp EEG due to muscle artifact. We applied Gabor Transform to evaluate 20 seizures from 8 consecutive patients admitted for video-EEG monitoring. We studied the relative intensity ratios of alpha, theta and delta bands over time. In 14 20 events we found a significant decremental activity in the delta band at the onset of the seizure indicating that this is dominated by theta and alpha bands. We conclude that GT is a useful auxiliary tool in the analysis of ictal activity that sheds light on the underlying pathophysiological mechanisms.

Negative dromotropic effects of Class I antiarrhythmic drugs in anisotropic ventricular muscle

In a computer simulation study to mimic cardiac action potential, the total open time of the sodium channel at each excitation has been shown by other authors to be longer during propagation parallel (longitudinal, L) to fiber orientation than perpendicular (transverse, T) to that. If this is the case in actual cardiac tissue, the Class I antiarrhythmic drug action on conduction would be affected by their mode of sodium channel block. The present study was designed to test this hypothesis. Effects of flecainide (F), quinidine (Q), aprindine (A) and SD3212 (S) on conduction velocity (theta), amplitude of extracellular potentials (phi e), and maximum upstroke velocity (Vmax) of action potentials were examined in isolated rabbit ventricular muscles with microscopic anisotropy. F (0.1-1 microM) or Q (2-10 microM), which blocks the sodium channel mainly during the activated state, caused a concentration- and frequency-dependent decrease in theta and phi e. The reduction was more prominent during L than T propagation, giving rise to a decrease in their anisotropic ratio (theta L/theta T). A (1-5 microM) or S (3-10 microM), which blocks the channel during the inactivated state, also decreased theta and phi e. However, the reduction was similar during L and T propagation, and the anisotropic ratio of theta and phi e remained unaffected. The decrease of maximum upstroke velocity (Vmax) of action potential by F or Q was greater during L than T propagation; VmaxL/VmaxT was decreased significantly. In contrast, the Vmax reduction by A(3 microM) or S (10 microM) was similar during L and T propagation. Different state-dependence of sodium channel block may underlie different negative dromotropic effects of Class I drugs in anisotropic cardiac muscle.

Theta Ratio - A Better Correlate of Anesthetic Depth

Theta Ratio - A Better Correlate of Anesthetic Depth

Limitations of EEG Frequency Analysis in the Diagnosis of Intracerebral Diseases

Publisher Summary This chapter discusses a study that is intended to determine whether abnormal electroencephalogram (EEG) findings obtained by quantitative EEG (qEEG) frequency analysis are necessarily related to the pathology of brain lesions. Quantitative EEG frequency analyses are made under experimental conditions of acute focal ischemia and experimentally induced brain tumors in various animals. In order to characterize significant features of the pathological EEG, other parameters such as blood flow, electrolyte homeostasis, and water content of the brain are also measured in the same animals. A specific relationship between EEG alterations and such parameters, prove to be applicable to the pathognomonic differentiation of the human cerebral brain lesions. The chapter describes EEG using qEEG analysis in patients suffering from cerebrovascular disease, brain tumors, intracerebral hemorrhage, and head trauma. Quantitative EEG frequency analysis determines the alterations of total EEG intensity, of the activity in conventional slow and fast wave bands and of the ratios of delta plus theta to alpha plus beta intensity (frequency index), which are related to changes of cerebral blood flow, electrolyte homeostasis and water content in experimental brain ischemia and brain tumors.

Trilayer Raman scattering of variably ordered amorphous Ge

Interference-enhanced Raman scattering measurements are reported on rf diode sputtered a-Ge as a function of annealing temperature. The results on films ∼50 Å thick indicate a monotonic decrease of the half-width of the TO-like phonon band for the depolarized Raman component as a function of annealing temperature. In addition, the ratio of the TA to TO peak intensities is also found to monotonically decrease with temperature. These results indicate changes in the vibrational spectrum of a-Ge that arise from increasing short range order and parallel studies on thicker a-Ge and a-Si films with deposition conditions. During crystallization the Raman spectra also indicate that the amorphous phase continues to increase its structural order. A comparison with the Raman spectra of thicker films allows an estimate of the optical gap to be obtained in the very thin a-Ge films.

Electron microprobe compositional analysis of sputtered tantalum-aluminium films

In the present paper the methods for measurement of the composition of two or more component tantalum-based thin sputtered films are summarized. The influence of the target construction on the composition of the films is discussed. The Ta-Al films were sputtered from composite Ta-Al targets. The composition of films was measured by means of the electron microprobe technique. From results it follows that using the composite targets for sputtering in argon at a pressure of 2×10−2 torr and in its mixture with nitrogen (10−3 torr), the composition of Ta-Al films is proportional to the ratio of the Ta and Al exposed surfaces on the target. The proportionality factor equals to the ratio of “effective” sputtering yields of target components measured at given sputtering conditions. The presence of nitrogen in sputtering gas decreases the value of Ta yield 2.2 times. If a small Al surface is sputtered together with much larger Ta surface, the sputtering yield of Al remains unchanged. In Ta-Al films the occluded argon was qualitatively determined. The presence of nitrogen was not proved. This seems to be caused by the absorption of nitrogen characteristic radiation in the investigated films.