Age-related characteristics of risky decision-making and progressive expectation formation

During daily encounters, it is inevitable that people take risks. Investigating the sequential processing of risk hazards involve expectation formation about outcome contingencies. The present study aimed to explore risk behavior and its neural correlates in sequences of decision making, particularly in old age, which represents a critical period regarding risk-taking propensity. The Balloon Analogue Risk Task was used in an electrophysiological setting with young and elderly age groups. During the task each additional pump on a virtual balloon increased the likelihood of a balloon burst but also increased the chance to collect more reward. Event-related potentials associated with rewarding feedback were analyzed based on the forthcoming decisions (whether to continue or to stop) in order to differentiate between states of expectation towards gain or loss. In the young, the reward positivity ERP component increased as a function of reward contingencies with the largest amplitude for rewarding feedback followed by the decision to stop. In the elderly, however, reward positivity did not reflect the effect of reward structure. Behavioral indices of risk-taking propensity suggest that the performance of the young and the elderly were dissociable only with respect to response times: The elderly was characterized by hesitation and more deliberative decision making throughout the experiment. These findings signify that sequential tracking of outcome contingencies has a key role in cost-efficient action planning and progressive expectation formation.

[ELECTROPHYSIOLOGIC ANALYSIS OF MENTAL ARITHMETIC TASK BY THE "MINIMUM SPANNING TREE" METHOD]

GOALS

In the present study basic arithmetic induced rearrangements in functional connections of the brain were investigated by using graph theoretical analysis what becomes increasingly important both in theoretical neuroscience and also in clinical investigations.

RESEARCH QUESTIONS

During mental arithmetic operations (working) memory plays an important role, but there are only a few studies in which an attempt was made to separate this effect from the process of arithmetic operations themselves. The goal of our study was to separate the neural networks involved in cognitive functions.

METHODS

As an attempt to clarify this issue the graph-theoretical "minimal spanning tree" method was used for the analysis of EEG recorded during task performance. The effects of passive viewing, number recognition and mental arithmetic on PLI based minimal spanning trees (MST) were investigated on the EEG in young adults (adding task: 17 subjects; passive viewing and number recognition: 16 subjects) in the θ (4-8 Hz) frequency band.

RESULTS

Occipital task relevant synchronization was found by using the different methods, probably related to the effect of visual stimulation. With respect to diameter, eccentricity and fraction of leafs different task-related changes were found.

DISCUSSION

It was shown that the task related changes of various graph indices are capable to identify networks behind the various relevant dominant functions. Thus the "minimal spanning tree" method is suitable for the analysis of the reorganization of the brain with respect to cognitive functions.

Age-related changes of frontal-midline theta is predictive of efficient memory maintenance

Frontal areas are thought to be the coordinators of working memory processes by controlling other brain areas reflected by oscillatory activities like frontal-midline theta (4-7 Hz). With aging substantial changes can be observed in the frontal brain areas, presumably leading to age-associated changes in cortical correlates of cognitive functioning. The present study aimed to test whether altered frontal-midline theta dynamics during working memory maintenance may underlie the capacity deficits observed in older adults. 33-channel EEG was recorded in young (18-26 years, N=20) and old (60-71 years, N=16) adults during the retention period of a visual delayed match-to-sample task, in which they had to maintain arrays of 3 or 5 colored squares. An additional visual odd-ball task was used to be able to measure the electrophysiological indices of sustained attentional processes. Old participants showed reduced frontal theta activity during both tasks compared to the young group. In the young memory maintenance-related frontal-midline theta activity was shown to be sensitive both to the increased memory demands and to efficient subsequent memory performance, whereas the old adults showed no such task-related difference in the frontal theta activity. The decrease of frontal-midline theta activity in the old group indicates that cerebral aging may alter the cortical circuitries of theta dynamics, thereby leading to age-associated decline of working memory maintenance function.

Frontal midline theta connectivity is related to efficiency of WM maintenance and is affected by aging

Representations in working memory (WM) are temporary, but can be refreshed for longer periods of time through maintenance mechanisms, thereby establishing their availability for subsequent memory tests. Frontal brain regions supporting WM maintenance operations undergo anatomical and functional changes with advancing age, leading to age related decline of memory functions. The present study focused on age-related functional connectivity changes of the frontal midline (FM) cortex in the theta band (4-8 Hz), related to WM maintenance. In the visual delayed-match-to-sample WM task young (18-26 years, N=20) and elderly (60-71 years N=16) adults had to memorize sample stimuli consisting of 3 or 5 items while 33 channel EEG recording was performed. The phase lag index was used to quantify connectivity strength between cortical regions. The low and high memory demanding WM maintenance periods were classified based on whether they were successfully maintained (remembered) or unsuccessfully maintained (unrecognized later). In the elderly reduced connectivity strength of FM brain region and decreased performance were observed. The connectivity strength between FM and posterior sensory cortices was shown to be sensitive to both increased memory demands and memory performance regardless of age. The coupling of frontal regions (midline and lateral) and FM-temporal cortices characterized successfully maintained trials and declined with advancing age. The findings provide evidence that a FM neural circuit of theta oscillations that serves a possible basis of active maintenance process is especially vulnerable to aging.

[Spectral, phase-synchronization, and graph theoretical EEG changes related to mental arithmetics]

During mental arithmetic operations working memory plays an important role, but there are only few studies in which an attempt was made to separate this effect from the process of arithmetics per se. In this study the effects of arithmetic on the EEG of young adults (14 participants, six of them women, mean age 21.57 years, SD: 2.62) was investigated during a subtraction task in the theta (4-8 Hz) frequency band. Besides the power density spectrum analysis phase synchrony based on recently developed graph theoretical methods were used and strength of local connections (cluster coefficient; C) and global interconnectedness of network (characteristic path length; L) were determined. Before the arithmetic task passive viewing (control situation) and a number recognition paradigms were used. During the arithmetic task compared to the control situation significantly increasing phase synchrony and C values were found. L was significantly shorter (F(2, 26) = 818.77, p < 0.0001) only during the arithmetic task: this fact and the former two results imply that the network topology shifted towards the "small world" direction. Our findings concerning regional differences confirm those reported earlier in the literature: compared to the control condition significant task-related increase was found in C values in the parietal areas [more explicitly in the left side, (F(1, 13) = 7.2020, p = 0.0188)], which probably corresponds to stronger local connections and more synchronized (sub)networks. During the task condition significantly increased 0 band power; (F(1, 13) = 7.9708, p = 0.01447 and decreased L values were found in the left frontal region compared to the right side (F(1, 13) = 6.0734, p = 0.0284), which can also be interpreted as an indicator of optimized network topology of information processing.

[Ageing and arithmetic performance--electrophysiological complexity-, and graph theoretical characteristics]

During the course of ageing the decline of cognitive performance, including attention and working memory processes--essential for arithmetic procedures--is well known. For the investigation of the neuronal mechanisms of these processes the application of methods capable of taking into account the high complexity of the nervous system, the role of nonlinear processes and network-properties of its constituents are necessary. As for the latter the recently realized small world network characteristics representing optimal conditions for information processing may be of particular importance. In the present study the spectral, complexity-, and network characteristics of the EEG recorded during performing an arithmetic task in a group of young (n=32, mean age 22.0 yrs) and elderly (n=19, mean age: 66.7 yrs) was analyzed. Heart rate and behavioral measures (number of mistakes, reaction time) were also investigated. The alpha2 band decreased in the young, while the delta band increased in the elderly in the task condition. The increased Omega-complexity observed in the elderly is probably caused by reduced interneuronal connectivity. "Small-world" network characteristics were found in the beta and delta bands although in the elderly the topology was closer to a random pattern. In the task condition the network features of the elderly subjects shifted more towards the small world pattern than those seen in the young indicating that for the elderly the mobilized effort for task completion was higher. In spite of this, the level of performance and the heart rate change observed in the elderly was lower than that seen in the young. The application of complexity-, and graph theoretical analysis appears to be a promising tool for the investigation of diseases of the nervous system characterized by diffuse pathology as in the case of as various types of dementias.

Age-dependent features of EEG-reactivity--spectral, complexity, and network characteristics

Our goal was to measure indices characterizing EEG-reactivity in young and elderly subjects. It was hypothesized that EEG-reactivity as reflected by different measures would be lower in the elderly. In two age groups (young: N= 23, mean age = 21.5 +/- 2.2 years; old: N= 25, mean age = 66.9 +/- 3.6 years) absolute frequency spectra, Omega-complexity, synchronization likelihood and network properties (clustering coefficient and characteristic path length) of the EEG were analyzed in the delta, theta, alpha1, alpha2, beta1 and beta2 frequency bands occurring as a result of eyes opening. Absolute spectral power was higher in the young in the delta, alpha1 and alpha2 bands in the posterior area. The alpha1 peak frequency decreased following eyes opening in the young, while no change was observed in the elderly. Omega-complexity was higher in the elderly especially in the frontal area and increased following eyes opening. Values of the clustering coefficient, path length and that of the "small-world index" decreased as a result of eyes opening, the latter in the fast frequency range. The results suggest reduced reactivity in the elderly as shown by frequency spectra and decreased level of integrative activity particularly in the frontal area probably as a result of reduced interneuronal processing capacity. Indices of network characteristics reveal a shift towards more random topology especially in the beta frequencies caused by eyes opening.

The Acute Effect of Alcohol on Various Memory Processes

This review surveys relevant and recent data of the pertinent literature regarding the acute effect of alcohol on various kinds of memory processes with special emphasis on working memory. The characteristics of different types of long-term memory (LTM) and short-term memory (STM) processes are summarized with an attempt to relate these to various structures in the brain. LTM is typically impaired by chronic alcohol intake but according to some data a single dose of ethanol may have long lasting effects if administered at a critically important age. The most commonly seen deleterious acute effect of alcohol to STM appears following large doses of ethanol in conditions of “binge drinking” causing the “blackout” phenomenon. However, with the application of various techniques and well-structured behavioral paradigms it is possible to detect, albeit occasionally, subtle changes of cognitive processes even as a result of a low dose of alcohol. These data may be important for the consideration of legal consequences of low-dose ethanol intake in conditions such as driving, etc.

The acute effect of low-dose alcohol on working memory during mental arithmetic: II. Changes of nonlinear and linear EEG-complexity in the theta band, heart rate and electrodermal activity

OBJECTIVE AND HYPOTHESIS

Nonlinear and linear methods of EEG-complexity analysis and autonomic measures were used to characterize processes accompanying performance in a mental arithmetic task challenged by low ("social") alcohol doses. It was expected that alcohol in such doses will dampen changes of task-related EEG-synchronization in the theta band, and those of heart rate and electrodermal activity (EDA).

METHODS

In the mental arithmetic task addition and working memory, effort was required. The EEG, ECG and EDA were recorded in 5 conditions: task, placebo-task, low dose-task (0.2 g/kg alcohol), high dose-task (0.4 g/kg alcohol). Omega-complexity and synchronization likelihood (SL) were computed of the theta band of the EEG.

RESULTS

Task-related decrease of the Omega-complexity and increase of the SL was found in the theta frequency band. Following alcohol consumption, these changes did not develop as seen especially for SL in the anterior area, although the significant effects were elicited by task performance. Conspicuous task-evoked increases were observed for ECG and EDA which were even more enhanced by alcohol.

CONCLUSIONS

Task-induced significant changes of the Omega-complexity and that of SL indicate increased synchrony in the theta band, probably corresponding to working memory effort. Both of these measures proved to be sensitive for the effect of low alcohol dose although these alcohol-elicited changes were not statistically significant. Task-induced heart rate and EDA increases were further intensified by alcohol probably indicating its activating effect on these autonomic measures in the dose range studied.