Jan Kamiński

Two Streams of Attention-Dependent β Activity in the Striate Recipient Zone of Cat's Lateral Posterior–Pulvinar Complex

Local field potentials from different visual cortical areas and subdivisions of the cats lateral posterior–pulvinar complex of the thalamus (LP-P) were recorded during a behavioral task based on delayed spatial discrimination of visual or auditory stimuli. During visual but not auditory attentive tasks, we observed an increase of β activity (12–25 Hz) as calculated from signals recorded from the caudal part of the lateral zone of the LP-P (LPl-c) as well as from cortical areas 17 and 18 and the complex located at the middle suprasylvian sulcus (MSS). This β activity appeared only in the trials that ended with a successful response, proving its relationship to the mechanism of visual attention. In contrast, no enhanced β activity was observed in the rostral part of the lateral zone of the LP-P and in the pulvinar proper. Two subregions of LPl-c (ventromedial and dorsolateral) were distinguished by visually related, attentional β activity of low (12–18 Hz) and high (18–25 Hz) frequencies, respectively. At the same time, area 17 exhibited attentional activation in the whole β range, and an increase of power in low-frequency β was observed in the medial bank of MSS, whereas cortical area 18 and the lateral bank of the MSS were activated in the high β range. Phase-correlation analysis revealed that two distinct corticothalamic systems were synchronized by the β activity of different frequencies. One comprised of cortical area 17, ventromedial region of LPl-c, and medial MSS, the second involved area 18 and the dorsolateral LPl-c. Our observations suggest that LPl-c belongs to the wide corticothalamic attentional system, which is functionally segregated by distinct streams of β activity.

Beta band oscillations engagement in human alertness process

We previously showed that neuronal activity in beta frequency might serve as a carrier for attentional arousal within the visual system of cat. In the present study, we adopted the animal paradigm for anticipatory attention to study alertness-related changes of beta activity in human subjects. The results indicated that increased alertness, manifested by faster responses to target visual stimuli, is accompanied by higher EEG activation in beta band.

Short-term memory capacity (7 ± 2) predicted by theta to gamma cycle length ratio

The number of items that can be held in human short-term memory (STM) is limited to 7 (± 2) elements. Lisman and Idiarts theoretical model of STM proposes that this value depends on the number of gamma cycles that can fit in one theta cycle. Previous studies on animals and humans provided support for this hypothesis but direct evidence from human EEG scalp recordings has not previously been reported. We recorded spontaneous EEG activity from 17 participants and measured their verbal STM capacity with a modified digit span task from the Wechsler battery. The strong and positive correlation we found between verbal STM capacity and theta/gamma cycle length ratio thus provides a direct argument in favor of this STM theoretical model. In this study we also demonstrated a new method for assessing individual theta and gamma frequencies by detecting functional coupling between these oscillations.

Beta band oscillations as a correlate of alertness — Changes in aging

Older adults (>60 years) show attentional deficits in comparison to younger people (18-30 years). As beta-band EEG activity has been previously postulated to indicate attentional modulation in the visual system, we searched for possible deficits in beta power in elderly subjects performing an attentional task with spatial differentiation between visual stimuli. We found that in older adults a lower level of beta activity correlated with decreased behavioral performance. As compared to young subjects, older adults expressed decreased activation in beta band during an attentional task, which displayed two different dynamics during the anticipatory period. Those dynamics were accompanied by one of two different behavioral pattern deficits. We hypothesize that one group of elderly participants suffered from difficulty in the activation of attentional processes (alertness deficits), while the other--from difficulty in sustaining those processes (vigilance deficits).

Information Transfer During a Transitive Reasoning Task

For about two decades now, the localization of the brain regions involved in reasoning processes is being investigated through fMRI studies, and it is known that for a transitive form of reasoning the frontal and parietal regions are most active. In contrast, less is known about the information exchange during the performance of such complex tasks. In this study, the propagation of brain activity during a transitive reasoning task was investigated and compared to the propagation during a simple memory task. We studied EEG transmission patterns obtained for physiological indicators of brain activity and determined whether there are frequency bands specifically related to this type of cognitive operations. The analysis was performed by means of the directed transfer function. The transmission patterns were determined in the theta, alpha and gamma bands. The results show stronger transmissions in theta and alpha bands from frontal to parietal as well as within frontal regions in reasoning trials comparing to memory trials. The increase in theta and alpha transmissions was accompanied by flows in gamma band from right posterior to left posterior and anterior sites. These results are consistent with previous neuroimaging (fMRI) data concerning fronto-parietal regions involvement in reasoning and working memory processes and also provide new evidence for the executive role of frontal theta waves in organizing the cognition.

Application of directed transfer function and network formalism for the assessment of functional connectivity in working memory task

The dynamic pattern of functional connectivity during a working memory task was investigated by means of the short-time directed transfer function. A clear-cut picture of transmissions was observed with the main centres of propagation located in the frontal and parietal regions, in agreement with imaging studies and neurophysiological hypotheses concerning the mechanisms of working memory. The study of the time evolution revealed that most of the time short-range interactions prevailed, whereas the communication between the main centres of activity occurred more sparsely and changed dynamically in time. The patterns of connectivity were quantified by means of a network formalism based on assortative mixing—an approach novel in the field of brain networks study. By means of application of the above method, we have demonstrated the existence of a modular structure of brain networks. The strength of interaction inside the modules was higher than between modules. The obtained results are compatible with theories concerning metabolic energy saving and efficient wiring in the brain, which showed that preferred organization includes modular structure with dense connectivity inside the modules and more sparse connections between the modules. The presented detailed temporal and spatial patterns of propagation are in line with the neurophysiological hypotheses concerning the role of gamma and theta activity in information processing during a working memory task.

Alertness opens the effective flow of sensory information through rat thalamic posterior nucleus

Behavioural reactions to sensory stimuli vary with the level of arousal, but little is known about the underlying reorganization of neuronal networks. In this study, we use chronic recordings from the somatosensory regions of the thalamus and cortex of behaving rats together with a novel analysis of functional connectivity to show that during low arousal tactile signals are transmitted via the ventral posteromedial thalamic nucleus (VPM), a first‐order thalamic relay, to the primary somatosensory (barrel) cortex and then from the cortex to the posterior medial thalamic nucleus (PoM), which plays a role of a higher‐order thalamic relay. By contrast, during high arousal this network scheme is modified and both VPM and PoM transmit peripheral input to the barrel cortex acting as first‐order relays. We also show that in urethane anaesthesia PoM is largely excluded from the thalamo‐cortical loop. We thus demonstrate a way in which the thalamo‐cortical system, despite its fixed anatomy, is capable of dynamically reconfiguring the transmission route of a sensory signal in concert with the behavioural state of an animal.

Information processing in brain and dynamic patterns of transmission during working memory task by the SDTF function

We studied the dynamical pattern of transmission involved in the information processing during cognitive experiments engaging working memory. The ensemble averaging approach was used to fit a multichannel autoregressive model to the EEG signals recorded during the transitive reasoning task. The short-time directed transfer function was estimated for finding dynamical patterns of functional connectivity during the memory and reasoning task. The results indicated that there exist particular areas where information is processed as envisaged by transmissions between closely located electrodes. In case of reasoning task these local circuits were located in frontal and parietal regions. These areas (these local circuits) from time to time exchange information between each other‥

The Time-Varying Causal Coupling in Brain and Organization of Its Networks

For investigation of time-varying brain networks an approach based on estimation of causal coupling by means of multivariate method was applied. Two cognitive experiments: Constant Attention Test and Working Memory task are considered. Time varying version of a multivariate estimator—Directed Transfer Function was used for calculating dynamically changing patterns of transmission during the tasks. Well-defined centers of activity congruent with imaging, anatomical and electrophysiological evidence were found. These centers exchanged the information only during short epochs. The strengths of coupling inside the tightly connected modules and between them was found by means of assortative mixing. The results point out to the well determined, far from randomness structure of brain networks in cognitive tasks. Very dense and disorganized structure of networks reported in literature may be explained by the presence of spurious connections produced by bi-variate measures of connectivity and further enhanced by giving all connections equal weights.