cognitive-function

Author: RYOHEI KIMURA, and TOSHIRO MURATA

The effects of i.p. administered theanine (L-N-ethylglutamine), a constituent of Japanese green tea, on the levels of norepinephrine (NE) and serotonin (5-HT) in the brain of rats with or without coadministration of caffeine were investigated, and compared with those of glutamine.Theanine decreased the NE level, whereas no change was observed with glutamine or caffeine.The decrease of NE induced by theanine was reversed by caffeine. In rats pretreated with pargline, a monoamine oxidase inhibitor, theanine significantly increased the NE level compared with the control. However, it did not enhance the NE levels increased by caffeine. Thus, theanine may decrease the NE levels by releasing this neurotransmitter.Theanine did not alter the levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in rats pretreated with or without pargyline, indicating that this amide affects neither 5-HT synthesis nor its degradation. Caffeine increased the levels of 5-HT and 5-HIAA in normal rats to similar extents.This effect was depressed by theanine. In rats pretreated with pargyline, the levels of 5-HT and 5-HIAA were not altered by caffeine, and theanine did not modify the outcome. It may be concluded that the action of theanine is related to the possible inhibition of 5-HT release by caffeine. The effect of glutamine on the levels of 5-HT was somewhat different form that of theanine.

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Author: W Klimesch and M Doppelmayr and H Russegger and T Pachinger and J Schwaiger

Induced alpha power (in a lower, intermediate and upper band) which is deprived from evoked electroencephalograph (EEG) activity was analyzed in an oddball task in which a warning signal (WS) preceded a target or non-target. The lower band, reflecting phasic alertness, desynchronizes only in response to the WS and target. The intermediate band, reflecting expectancy, desynchronizes about 1 s before a target or non-target appears. Upper alpha desynchronizes only after a target is presented and, thus, reflects the performance of the task which was to count the targets. Thus, only slower alpha frequencies reflect attentional demands such as alertness and expectancy.

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Author: Simon P. Kelly and Edmund C. Lalor and Richard B. Reilly and John J. Foxe

Human electrophysiological (EEG) studies have demonstrated the involvement of alpha band (8- to 14-Hz) oscillations in the anticipatory biasing of attention. In the context of visual spatial attention within bilateral stimulus arrays, alpha has exhibited greater amplitude over parietooccipital cortex contralateral to the hemifield required to be ignored, relative to that measured when the same hemifield is to be attended. Whether this differential effect arises solely from alpha desynchronization (decreases) over the “attending” hemisphere, from synchronization (increases) over the “ignoring” hemisphere, or both, has not been fully resolved. This is because of the confounding effect of externally evoked desynchronization that occurs involuntarily in response to visual cues. Here, bilateral flickering stimuli were presented simultaneously and continuously over entire trial blocks, such that externally evoked alpha desynchronization is equated in precue baseline and postcue intervals. Equivalent random letter sequences were superimposed on the left and right flicker stimuli. Subjects were required to count the presentations of the target letter “X” at the cued hemifield over an 8-s period and ignore the sequence in the opposite hemifield. The data showed significant increases in alpha power over the ignoring hemisphere relative to the precue baseline, observable for both cue directions. A strong attentional bias necessitated by the subjective difficulty in gating the distracting letter sequence is reflected in a large effect size of 2.1 (η2 = 0.82), measured from the attention × hemisphere interaction. This strongly suggests that alpha synchronization reflects an active attentional suppression mechanism, rather than a passive one reflecting “idling” circuits.

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Author: Kelly SP, and Lalor EC, and Reilly RB, and Foxe JJ

The steady-state visual evoked potential (SSVEP) has been employed successfully in brain-computer interface (BCI) research, but its use in a design entirely independent of eye movement has until recently not been reported. This paper presents strong evidence suggesting that the SSVEP can be used as an electrophysiological correlate of visual spatial attention that may be harnessed on its own or in conjunction with other correlates to achieve control in an independent BCI. In this study, 64-channel electroencephalography data were recorded from subjects who covertly attended to one of two bilateral flicker stimuli with superimposed letter sequences. Offline classification of left/right spatial attention was attempted by extracting SSVEPs at optimal channels selected for each subject on the basis of the scalp distribution of SSVEP magnitudes. This yielded an average accuracy of approximately 71% across ten subjects (highest 86%) comparable across two separate cases in which flicker frequencies were set within and outside the alpha range respectively. Further, combining SSVEP features with attention-dependent parieto-occipital alpha band modulations resulted in an average accuracy of 79% (highest 87%).

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Author: Gomez-Ramirez M, and Higgins BA, and Rycroft JA, and Owen GN, and Mahoney J, and Shpaner M, and Foxe JJ

OBJECTIVE: : Ingestion of the nonproteinic amino acid theanine (5-N-ethylglutamine) has been shown to increase oscillatory brain activity in the so-called alpha band (8-14 Hz) during resting electroencephalographic recordings in humans. Independently, alpha band activity has been shown to be a key component in selective attentional processes. Here, we set out to assess whether theanine would cause modulation of anticipatory alpha activity during selective attentional deployments to stimuli in different sensory modalities, a paradigm in which robust alpha attention effects have previously been established. METHODS: : Electrophysiological data from 168 scalp electrode channels were recorded while participants performed a standard intersensory attentional cuing task. RESULTS: : As in previous studies, significantly greater alpha band activity was measured over parieto-occipital scalp for attentional deployments to the auditory modality than to the visual modality. Theanine ingestion resulted in a substantial overall decrease in background alpha levels relative to placebo while subjects were actively performing this demanding attention task. Despite this decrease in background alpha activity, attention-related alpha effects were significantly greater for the theanine condition. CONCLUSION: : This increase of attention-related anticipatory alpha over the right parieto-occipital scalp suggests that theanine may have a specific effect on the brain's attention circuitry. We conclude that theanine has clear psychoactive properties, and that it represents a potentially interesting, naturally occurring compound for further study, as it relates to the brain's attentional system.

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Effects of l-theanine on attention and reaction time response

Author: Akiko Higashiyama and Hla Hla Htay and Makoto Ozeki and Lekh R.Juneja and Mahendra P.Kapoor

Previous human studies revealed that l-theanine influences brain function. The current study was designed to evaluate the affect of l-theanine (Suntheanine®) on attention and reaction time response in 18 normal healthy University student volunteers. In accordance with preliminary analysis of the manifest anxiety scale (MAS), the subjects were divided into two groups referred to as high anxiety propensity group and the minimal anxiety propensity group. Both groups received l-theanine (200 mg/100 ml water) and placebo (100 ml water) in a double blind repeated measurement design protocol. Assessments were performed for 15–60 min after consumption under a relaxed condition upon exerting an experimentally induced visual attentional task as well as audio response tests. Self-reports of anxiety as State-Trait Anxiety Inventory (STAI) was characterized at post experiments. Alpha bands electroencephalographic activity and heart rate were recorded throughout the trial. The results demonstrate the significant enhanced activity of alpha bands, descending heart rate, elevated visual attentional performance, and improved reaction time response among high anxiety propensity subjects compared to a placebo. However, no significant differences were noticed among subjects with a minimal anxiety propensity. Results evidently demonstrated that l-theanine clearly has a pronounced effect on attention performance and reaction time response in normal healthy subjects prone to have high anxiety.

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Author: Song CH, and Jung JH, and Oh JS, and Kim KS

L-theanine Is an amino acid in green tea and has been known to decrease serotonin and increase norepinephrine in rat brains, and also reported to produce mental relaxation, lower blood pressure and improve learning ability in human beings. But, few studies on these effects for human beings have been conducted so far. This study was conducted to evaluate the effect of L-theanine on the release of brain alpha waves known to be related with mental relaxation and concentration. Twenty healthy male volunteers aged 18 to 30 years without any Physical and Psychological diseases were recruited through written advertisement. Alpha power values of EEG as a surrogate marker of mental relaxation and concentration were measured in frontal and occipital regions for 40 minutes after administration of four placebo or test tablets and 20 minute resting period. The same procedure crossed over at 7-day intervals. We analyzed average alpha power values in frontal and occipital regions at 10 minute intervals. Repeated ANOVA revealed that there were significant differences of occipital alpha power values between placebo and test groups with high anxiety (p<0.05). The mean values at 20,30,40,50 and 60 minute intervals were 0.23, 024, 0.28, 0.25 and 0.34 in placebo, respectively and 0.23, 0.29, 0.40, 0.34, and 0.45 in test, respectively. But there were no significant differences of frontal and occipital alpha power values between placebo and test groups with low anxiety (p>0.05) . The results of this study suggest that L-theanine containing tablets promote the release of alpha waves related to mental relaxation and concentration in young adult males.

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Author: Tamano H, and Fukura K, and Suzuki M, and Sakamoto K, and Yokogoshi H, and Takeda A. 

Theanine, γ-glutamylethylamide, is one of the major amino acid components in green tea. On the basis of the preventive effect of theanine intake after birth on mild stress-induced attenuation of hippocamapal CA1 long-term potentiation (LTP), the present study evaluated the effect of theanine intake after weaning on stress-induced impairments of LTP and recognition memory. Young rats were fed water containing 0.3% theanine for 3 weeks after weaning and subjected to water immersion stress for 30 min, which was more severe than tail suspension stress for 30 s used previously. Serum corticosterone levels were lower in theanine-administered rats than in the control rats even after exposure to stress. CA1 LTP induced by a 100-Hz tetanus for 1 s was inhibited in the presence of 2-amino-5-phosphonovalerate (APV), an N-methyl-d-aspartate (NMDA) receptor antagonist, in hippocampal slices from the control rats and was attenuated by water immersion stress. In contrast, CA1 LTP was not significantly inhibited in the presence of APV in hippocampal slices from theanine-administered rats and was not attenuated by the stress. Furthermore, object recognition memory was impaired in the control rats, but not in theanine-administered rats. The present study indicates the preventive effect of theanine intake after weaning on stress-induced impairments of hippocampal LTP and recognition memory. It is likely that the modification of corticosterone secretion after theanine intake is involved in the preventive effect.

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Author: RYOHEI KIMURA, and TOSHIRO MURATA

Theanine (N-ethylglutamine), a flavourous constituent of tea leaves, was studied in respect of the influence on the central nervous system in mice.
Theanine was shown to inhibit the convulsive action of caffeine, but was ineffective against pentetrazole, picrotoxin, strychnine, pipradrol and bemegride as well as L-glutamine. Neither theanine nor L-glutamine effected on the prolongation of the sleeping time after the injection of hexobarbital sodium in mice. Using 14C-labeled theanine, it was found that the intraperitoneally administered theanine was taken up by brain tissue with out undergoing the metabolic changes in a 30minutes. The intracerebral level of γaminobutyric acid was shown to increase significantly at 30minutes following the intraperitoneal administration of theanine in mice.

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Author: Kim Zarse and Saskia Jabin and Michael Ristow