Aneta Brzezicka

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.

Working memory capacity as a moderator of load-related frontal midline theta variability in Sternberg task.

The aim of this study was to investigate the relationship between working memory capacity (WMC) and frontal theta response to memory load in Sternberg task. We show that oscillatory activity in the theta band (4–6 Hz) related to Sternberg task performance may differentiate people characterized by high and low WMC. Specifically, there is a linear increase of frontal midline (FM) theta power with load, however, only in the high WMC group. Furthermore, a positive linear relationship was found between WMC (operation span task score) and average FM theta power increase from lower to higher loads which was not present at other scalp locations. The distinct patterns of high and low WMC individual’s FM theta response to memory load seem to support the assumption that theta activity during maintenance reflects not only the amount of information stored, but also the effort it takes to remember them and the efficiency of involved neural processes. This contributes to perceiving FM theta as an individual trait which can reflect individual working memory mechanism efficiency.

Involvement of retrosplenial cortex in classical conditioning

The cingulate cortex, which comprises of two major subdivisions - anterior cingulate cortex (CG) and retrosplenial cortex (RSP), is implicated in many cognitive functions. The RSP is an important node in the systemic integration network. Studies point to its role in learning that involves spatial stimuli and navigation. Relatively little is known about its involvement in simple learning such as classical conditioning. We examined the involvement of the two cytoarchitectonic divisions, agranular and granular, of the rostral and caudal RSP in a delay conditioning, where stimulation of the facial vibrissae was paired with a tail shock. During the conditioning session the [(14)C]-2-deoxyglucose (2DG) brain mapping was performed. Effectiveness of conditioning was assessed with frequency of head movements, which decreased in the course of the conditioning. 2DG uptake in RSP and additionally in CG was examined in conditioned, pseudoconditioned and stimulated control groups. The metabolic labeling was elevated in caudal and rostral both RSP and CG in the conditioned group, but not in animals which received CS or UCS alone. Comparison between conditioned and pseudoconditioned groups showed the specific activation by associative learning in both divisions of the rostral RSP and rostral CG. Counts of c-Fos expressing nuclei confirmed activation of the rostral RSP in the CS+UCS group. These data support the concept of RSP as structure that, besides its recognized role in visuospatial learning, monitors and reacts to activity of brain systems responsible for other types of learning and, together with CG, subserve cognitive processes, with simple associative learning among them.

The unique cognitive limitation in subclinical depression: the impairment of mental model construction

The notion of “depression” is frequently employed to describe a broader category of depressive symptoms, dysphoria, and the depression syndrome as such (Joormann, 2005). Numerous debates in the literature have addressed the issue of continuity, the question of whether moderate depression symptoms (called subclinical depression) differ quantitatively or qualitatively from severe clinical depression. Flett, Vredenburg, and Kramses (1997) drew up a summary indicating that the available data is generally consistent with the hypothesis of continuity. In this chapter, we review data from studies in which subclinical forms of depressive disorders were taken into account: those that are mild in terms of severity. Depression is then seen as an affective disorder characterized by persistent negative mood (without an elevated level of arousal) and specific deficits in cognitive functioning. These deficits include “ruminative” thinking, recurring ideas and thoughts with negative or self-devaluing content. Such deficits also involve individuals with depression experiencing difficulty in solving complex cognitive problems, and solving problems that require reasoning about deeper social relations.

Frontal EEG alpha band asymmetry as a predictor of reasoning deficiency in depressed people

ABSTRACT Cognitive deficits in depression are mostly apparent in executive functions, especially when integration of information and reasoning is required. In parallel, there are also numerous studies pointing to the frontal alpha band asymmetry as a psychophysiological marker of depression. In this study, we explored the role of frontal alpha asymmetry as a potential factor explaining the cognitive problems accompanying depression. Twenty-six depressed and 26 control participants completed a reasoning task and underwent 5 minutes of electroencephalography recording. In line with the previous studies, depressed people showed difficulties with reasoning but we did not observe the relationship between frontal asymmetry in the alpha band and depression. However, we found that in the depressed group the frontal alpha asymmetry index was characterised by larger variance than in the control group, and it was also a strong predictor of cognitive functioning exclusively in the depressed group. Our results point to the disruption of a psychophysiological balance, reflected in changed frontal alpha asymmetry (into more left-sided frontal asymmetry in the alpha band, reflecting more right-sided cortical activity) as a possible brain correlate of cognitive disturbances present in depressive disorders.

Eye movement evidence for defocused attention in dysphoria — A perceptual span analysis

The defocused attention hypothesis (von Hecker and Meiser, 2005) assumes that negative mood broadens attention, whereas the analytical rumination hypothesis (Andrews and Thompson, 2009) suggests a narrowing of the attentional focus with depression. We tested these conflicting hypotheses by directly measuring the perceptual span in groups of dysphoric and control subjects, using eye tracking. In the moving window paradigm, information outside of a variable-width gaze-contingent window was masked during reading of sentences. In measures of sentence reading time and mean fixation duration, dysphoric subjects were more pronouncedly affected than controls by a reduced window size. This difference supports the defocused attention hypothesis and seems hard to reconcile with a narrowing of attentional focus.