Lateralized ultradian rhythms in time and space: a chronobiological field study in Kenyan Maasai.

Lateralized ultradian rhythms oscillating separately in the right and left hemispheres of the human brain can be monitored by variations in the tactile discrimination of either hand. A previous study in male German subjects has shown that the tactile error rates determined for the right and left hands oscillate with significantly different periodicities. In the present study, a group of Kenyan Maasai shepherds was tested while the subjects were leading herds on daily feeding routes. The Maasai exhibit considerable ultradian rhythms of about 2 hours in tactile error rates of either hand, but in contrast to the German subjects there is no significant difference between the right and left side. While an individual is en route, his hemispheres proceed through alternating states in matching segments of the path. Ultradian rhythms thus 'scan' not only the time of day but also the space, and might provide an intrinsic time-frame for neuronal processes of cognitive mapping.     

Ultradian and Asymmetric Rhythms of Hemispheric Processing Speed

Daily changes in cognitive performance have been documented, both in time of day/effect paradigm studies and in time‐isolation studies. However, in both types of studies, phenomena such as the “post‐lunch dip” have been found that were difficult to explain in terms of theoretical backgrounds. These phenomena may suggest ultradian rhythms in cognitive performance. A number of studies have also shown ultradian and asymmetric rhythms in activity indices of the brain hemispheres. The aim of this study was to test three hypotheses: the first two assumed that there is a significant ultradian frequency in a component of the endogenous rhythm of processing speed, and the third assumed that the ultradian endogenous rhythms of the processing speed (encoding and recognition) of stimuli addressed to the left brain hemisphere differ in period length from those addressed to right hemisphere. During a 24 h constant‐routine experiment, the memory performance of 30 participants was measured eight times (every 2.5–3 h), starting at 06:30 h. Parallel sets of words and pictures were shown to subjects in a random order in either the left or the right visual field on a computer screen. The participants pressed one of two buttons in response to the picture or word, or when answering a question concerning the meaning of a presented stimulus. Cosinor analysis was applied to individual time series data. Two significant ultradian components were found in a majority of the time series. Dominant periods were analyzed using three factor ANOVA. The results showed an asymmetry between both hemispheres in the frequency of ultradian rhythms in encoding speed.     

Ultradian and asymmetric rhythms of hemispheric processing speed

Daily changes in cognitive performance have been documented, both in time of day/effect paradigm studies and in time-isolation studies. However, in both types of studies, phenomena such as the “post-lunch dip” have been found that were difficult to explain in terms of theoretical backgrounds. These phenomena may suggest ultradian rhythms in cognitive performance. A number of studies have also shown ultradian and asymmetric rhythms in activity indices of the brain hemispheres. The aim of this study was to test three hypotheses: the first two assumed that there is a significant ultradian frequency in a component of the endogenous rhythm of processing speed, and the third assumed that the ultradian endogenous rhythms of the processing speed (encoding and recognition) of stimuli addressed to the left brain hemisphere differ in period length from those addressed to right hemisphere. During a 24 h constant-routine experiment, the memory performance of 30 participants was measured eight times (every 2.5-3 h), starting at 06:30 h. Parallel sets of words and pictures were shown to subjects in a random order in either the left or the right visual field on a computer screen. The participants pressed one of two buttons in response to the picture or word, or when answering a question concerning the meaning of a presented stimulus. Cosinor analysis was applied to individual time series data. Two significant ultradian components were found in a majority of the time series. Dominant periods were analyzed using three factor ANOVA. The results showed an asymmetry between both hemispheres in the frequency of ultradian rhythms in encoding speed.     

Ultradian rhythms in processing speed of laterally exposed words and pictures

The study was designed to find out the cerebral hemispheres oscillations in stimuli processing during the 24-hour period of wakefulness in isolated subjects remaining in a monotonous environment. Stimuli processing speed from the 24-hour constant routine periods (06.00-06.00 h) of a larger experiment were analysed for the purpose of this paper. Parallel sets of words and pictures were exposed laterally using a purpose-designed computer program. The subjects reacted to pictures or words by pressing appropriate buttons. The significant dominant ultradian rhythms (around 4 h) in the processing speed of words addressed to the right hemisphere were found and of pictures addressed to the left hemisphere. Longer significant dominant periodicities (around 12 h) appeared in the processing speed of words addressed to the left hemisphere and of pictures (around 8 h) addressed to the right hemisphere. Ultradian rhythmicity of the central nervous system functioning is suggested.     

Left and right brain hemispheres in the regulation of pain sensitivity biorhythms in mice during stress

The foot-shock effects on ultradian and circadian rhythms of pain sensitivity in the SHR mice were studied after unilateral brain cortex hemisphere inactivation by means of the Leao spreading depression. Under acute painful stress, the left hemisphere partially loses its synchronizing effect on circadian rhythm and supports the 12-hour and particularly 6-hour periodicities. The left hemisphere effect dominates in intact animals under stress. The right hemisphere under the same conditions mainly loses its activating effect on circadian rhythm and supports the 8- and 16-hour periodicities. The right hemisphere effect dominates in animals under stress operated 2-3 days prior to the experiment.     

Sustained Spatial Attention to Vibrotactile Stimulation in the Flutter Range: Relevant Brain Regions and Their Interaction

The present functional magnetic resonance imaging (fMRI) study was designed to get a better understanding of the brain regions involved in sustained spatial attention to tactile events and to ascertain to what extent their activation was correlated. We presented continuous 20 Hz vibrotactile stimuli (range of flutter) concurrently to the left and right index fingers of healthy human volunteers. An arrow cue instructed subjects in a trial-by-trial fashion to attend to the left or right index finger and to detect rare target events that were embedded in the vibrotactile stimulation streams. We found blood oxygen level-dependent (BOLD) attentional modulation in primary somatosensory cortex (SI), mainly covering Brodmann area 1, 2, and 3b, as well as in secondary somatosensory cortex (SII), contralateral to the to-be-attended hand. Furthermore, attention to the right (dominant) hand resulted in additional BOLD modulation in left posterior insula. All of the effects were caused by an increased activation when attention was paid to the contralateral hand, except for the effects in left SI and insula. In left SI, the effect was related to a mixture of both a slight increase in activation when attention was paid to the contralateral hand as well as a slight decrease in activation when attention was paid to the ipsilateral hand (i.e., the tactile distraction condition). In contrast, the effect in left posterior insula was exclusively driven by a relative decrease in activation in the tactile distraction condition, which points to an active inhibition when tactile information is irrelevant. Finally, correlation analyses indicate a linear relationship between attention effects in intrahemispheric somatosensory cortices, since attentional modulation in SI and SII were interrelated within one hemisphere but not across hemispheres. All in all, our results provide a basis for future research on sustained attention to continuous vibrotactile stimulation in the range of flutter.     

Molecular approaches to brain asymmetry and handedness

In the human brain, distinct functions tend to be localized in the left or right hemispheres, with language ability usually localized predominantly in the left and spatial recognition in the right. Furthermore, humans are perhaps the only mammals who have preferential handedness, with more than 90% of the population more skillful at using the right hand, which is controlled by the left hemisphere. How is a distinct function consistently localized in one side of the human brain? Because of the convergence of molecular and neurological analysis, we are beginning to consider the puzzle of brain asymmetry and handedness at a molecular level.     

Characteristics of the interhemispheric EEG relationships in assessing the functional state of the human brain

In healthy subjects (11 right-handed men) reorganization was studied of intra- and interhemispheric correlation of the electrical brain activity at transition from the state of alertness to drowsiness. At the lowering of alertness level, the coherence of hemispheres symmetrical points changed not abruptly, with a tendency towards an increase at differently directed character of changes of combinations of separate physiological rhythms ranges. Comparison of the EEG coherence changes within the right and left hemispheres revealed a greater reactivity of the left (dominant) hemisphere. The reduction of the predominance (observed in the dominant hemisphere in alertness) of the degree of EEG conjunction, at transition to drowsiness, leads to smoothing of interhemispheric asymmetry in the organization of electrical brain processes.     

Getting a Grip on Memory: Unilateral Hand Clenching Alters Episodic Recall

Unilateral hand clenching increases neuronal activity in the frontal lobe of the contralateral hemisphere. Such hand clenching is also associated with increased experiencing of a given hemisphere’s “mode of processing.” Together, these findings suggest that unilateral hand clenching can be used to test hypotheses concerning the specializations of the cerebral hemispheres during memory encoding and retrieval. We investigated this possibility by testing effects of unilateral hand clenching on episodic memory. The hemispheric Encoding/Retrieval Asymmetry (HERA) model proposes left prefrontal regions are associated with encoding, and right prefrontal regions with retrieval, of episodic memories. It was hypothesized that right hand clenching (left hemisphere activation) pre-encoding, and left hand clenching (right hemisphere activation) pre-recall, would result in superior memory. Results supported the HERA model. Also supported was that simple unilateral hand clenching can be used as a means by which the functional specializations of the cerebral hemispheres can be investigated in intact humans.     

Ultradian rhythms in the EEG and task performance

The purpose of this work was to investigate the presence of ultradian rhythms in: 1. levels of electroencephalographic activation; 2. interhemispheric correlation and 3. the performance of two cognitive tasks, and the correlation between these variables. Eight volunteers, aged 20 to 30, participated in the experiment. Two sessions were carried out: one from 0800 to 1400 on one day and the other from 1400 to 2000 another day. Samples of EEG activity were taken every 15 min at rest with eyes open in left and right temporal, central, parietal and occipital derivations referred to the ipsilateral earlobe the performance on two tasks, one logico-analytical (left hemisphere functions) and one spatial test (right hemisphere functions) was assessed. As control, body and environmental temperature were recorded. To test for the presence of ultradian rhythms, the data were subjected to a Fourier analysis. Different EEG variables showed rhythmicity throughout the sessions, principally with slow oscillation periods (3 and 6h); ultradian rhythms with 3h periods were also found in body temperature, while task performance showed no significant rhythmic patterns during sessions. Finally, no significant correlations were found between physiological variables evaluated and task performance.     

On Disturbances of Interhemispheric Interaction in Psychopathologic States (Development of Ideas of L.Ya. Balonov and V.L. Deglin)

The current state of the problem of changes of brain functional asymmetry in psychopathology is reviewed from the point of view of disorders of interhemispheric interaction as the main chain in genesis of affective disorders and schizophrenia. Based on studies of individual activation of the left and right hemispheres as well as on evaluation of cognitive activity, it is shown that psychopathology is accompanied by a disorder of hemispheric interaction with shift of the interhemispheric activation balance towards the right hemisphere in depression and towards the left hemisphere in maniacal states and paranoid schizophrenia. Changes of the activation balance lead to disorder of cognitive activity and human adaptation in the environment. A conclusion is made that disinhibition of subcortical and brainstem structures in psychoses occurs not only vertically, but also horizontally, when the complementary and superpositional interaction of hemispheres shifts to the evolutionary earlier reciprocal type of interaction with domination of cognitive functions of the right hemisphere in depression and of the left hemisphere in the maniacal state and schizophrenia.     

Diurnal emotional reactivity: Ultradian changes at neural and behavioral levels in men

The aim of this study was to examine the ultradian dynamic of emotional processing in men. Event-related potentials were recorded while participants watched different sets of unpleasant and neutral pictures every 15?min for 3?h. Emotional feelings induced by unpleasant pictures were also assessed with self-rating scales at the end of each picture set. Whereas brain processing of neutral pictures remained stable over time, a late positive component elicited by unpleasant pictures presented ultradian oscillations varying between 65 and 110?min in 77% of the participants, mainly in the right centro-posterior area. Ultradian rhythms were also observed for values self-rating the intensity of unpleasant feelings. Correlative analyses performed between brain and behavioral ultradian oscillations indicated that these rhythms follow a temporal opposite pattern. For the first time, these results raise questions regarding the modulating role of ultradian oscillations when the brain computes the significance of unpleasant stimuli and produces the final emotional feelings. Overall, these findings open new perspectives on the temporal regulation of emotional reactivity in healthy individuals and in those with affective disorders.     

Hemispheric specialization in dogs for processing different acoustic stimuli

Considerable experimental evidence shows that functional cerebral asymmetries are widespread in animals. Activity of the right cerebral hemisphere has been associated with responses to novel stimuli and the expression of intense emotions, such as aggression, escape behaviour and fear. The left hemisphere uses learned patterns and responds to familiar stimuli. Although such lateralization has been studied mainly for visual responses, there is evidence in primates that auditory perception is lateralized and that vocal communication depends on differential processing by the hemispheres. The aim of the present work was to investigate whether dogs use different hemispheres to process different acoustic stimuli by presenting them with playbacks of a thunderstorm and their species-typical vocalizations. The results revealed that dogs usually process their species-typical vocalizations using the left hemisphere and the thunderstorm sounds using the right hemisphere. Nevertheless, conspecific vocalizations are not always processed by the left hemisphere, since the right hemisphere is used for processing vocalizations when they elicit intense emotion, including fear. These findings suggest that the specialisation of the left hemisphere for intraspecific communication is more ancient that previously thought, and so is specialisation of the right hemisphere for intense emotions.     

Marijuana: Differential effects on right and left hemisphere functions in man

Marijuana, smoked at moderate doses, produced a differential impairment of the reaction times of right-handed males to pictorial stimuli presented to the left and right cerebral hemispheres. After smoking marijuana responses to pictorial stimuli presented to the right hemisphere were slowed significantly less than to the left hemisphere. Responses to verbal stimuli (trigrams) were slowd equally in both hemispheres, preserving an initial left hemisphere superiority for this material. This suggests that marijuana may differentially change the processing speed or relative dominance of man's two cerebral hemispheres, depending on the nature of the material being processed.     

Assessment of recognition of emotions by healthy persons and patients with focal brain pathology

To assess the involvement of different structures of the human brain into successive stages of the recognition of the principal emotions by facial expression, we examined 48 patients with local brain lesions and 18 healthy adult subjects. It was shown that at the first (intuitive) stage of the recognition, premotor areas of the right hemisphere and temporal areas of the left hemisphere are of considerable importance in the recognition of both positive and negative emotions. In this process, the left temporal areas are substantially involved into the recognition of anger, and the right premotor areas predominantly participate in the recognition of fear. In patients with lesions of the right and left brain hemispheres, at the second (conscious) stage of recognition, the critical attitude to the assessment of emotions drops depending on the sign of the detected emotion. We have confirmed the hypothesis about a correlation between the personality features of the recognition of facial expressions and the dominant emotional state of a given subject.     

Electrical Correlate of Right Hemisphere Function

IN right handed individuals, the two cerebral hemispheres seem to be specialized for different functions. The role of the left hemisphere in controlling language and the preferred hand is well known, but the specialization of the right hemisphere has proved harder to define¹. The effects of unilateral cortical damage and, in particular, right temporal resections² have led to the view that the right hemisphere is concerned with analysis of complex visuo-spatial patterns. This view is supported by work on brain bisected patients³ and by tachistoscopic studies such as those of Durnford and Kimura⁴.     

Cerebral Asymmetry of fMRI-BOLD Responses to Visual Stimulation

Hemispheric asymmetry of a wide range of functions is a hallmark of the human brain. The visual system has traditionally been thought of as symmetrically distributed in the brain, but a growing body of evidence has challenged this view. Some highly specific visual tasks have been shown to depend on hemispheric specialization. However, the possible lateralization of cerebral responses to a simple checkerboard visual stimulation has not been a focus of previous studies. To investigate this, we performed two sessions of blood-oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) in 54 healthy subjects during stimulation with a black and white checkerboard visual stimulus. While carefully excluding possible non-physiological causes of left-to-right bias, we compared the activation of the left and the right cerebral hemispheres and related this to grey matter volume, handedness, age, gender, ocular dominance, interocular difference in visual acuity, as well as line-bisection performance. We found a general lateralization of cerebral activation towards the right hemisphere of early visual cortical areas and areas of higher-level visual processing, involved in visuospatial attention, especially in top-down (i.e., goal-oriented) attentional processing. This right hemisphere lateralization was partly, but not completely, explained by an increased grey matter volume in the right hemisphere of the early visual areas. Difference in activation of the superior parietal lobule was correlated with subject age, suggesting a shift towards the left hemisphere with increasing age. Our findings suggest a right-hemispheric dominance of these areas, which could lend support to the generally observed leftward visual attentional bias and to the left hemifield advantage for some visual perception tasks.     

The Lateralizer: a tool for students to explore the divided brain

Despite a profusion of popular misinformation about the left brain and right brain, there are functional differences between the left and right cerebral hemispheres in humans. Evidence from split-brain patients, individuals with unilateral brain damage, and neuroimaging studies suggest that each hemisphere may be specialized for certain cognitive processes. One way to easily explore these hemispheric asymmetries is with the divided visual field technique, where visual stimuli are presented on either the left or right side of the visual field and task performance is compared between these two conditions; any behavioral differences between the left and right visual fields may be interpreted as evidence for functional asymmetries between the left and right cerebral hemispheres. We developed a simple software package that implements the divided visual field technique, called the Lateralizer, and introduced this experimental approach as a problem-based learning module in a lower-division research methods course. Second-year undergraduate students used the Lateralizer to experimentally challenge and explore theories of the differences between the left and right cerebral hemispheres. Measured learning outcomes after active exploration with the Lateralizer, including new knowledge of brain anatomy and connectivity, were on par with those observed in an upper-division lecture course. Moreover, the project added to the students' research skill sets and seemed to foster an appreciation of the link between brain anatomy and function.     

Effects of peptide factors from right and left brain hemispheres of rats on amplitude-time characteristics of projective and interhemispheric evoked responses

Peptide extracts of the right and left hemispheres were applied to the projective (somatosensory and visual) and temporal associative regions of the left brain hemisphere in cats. In the zones of peptide application, evoked potentials (EP) in response to singular and coupled somatic, visual and transcallosal stimuli were registered. The data obtained showed that right and left peptide extracts had different effects on evoked potentials of the left hemisphere. Thus ipsilateral extract increased the amplitude of projective EP, decreased duration of their cycles and amplitude of transcallosal responses. Contralateral extract, on the contrary, activated interhemispheric inputs to brain cortex, suppressed thalamic inputs and increased multimodal properties of neurons. A differential approach to the problem of specific correction of pathological states of the right and left brain hemispheres is required. Right and left peptide extracts may be used in normalization of interhemispheric activity balance in compensatory-recovering processes.     

Visual Hierarchical Processing and Lateralization of Cognitive Functions through Domestic Chicks' Eyes

Hierarchical stimuli have proven effective for investigating principles of visual organization in humans. A large body of evidence suggests that the analysis of the global forms precedes the analysis of the local forms in our species. Studies on lateralization also indicate that analytic and holistic encoding strategies are separated between the two hemispheres of the brain. This raises the question of whether precedence effects may reflect the activation of lateralized functions within the brain. Non-human animals have perceptual organization and functional lateralization that are comparable to that of humans. Here we trained the domestic chick in a concurrent discrimination task involving hierarchical stimuli. Then, we evaluated the animals for analytic and holistic encoding strategies in a series of transformational tests by relying on a monocular occlusion technique. A local precedence emerged in both the left and the right hemisphere, adding further evidence in favour of analytic processing in non-human animals.