Age effects on EEG correlates of the Wisconsin Card Sorting Test

Abstract

Body and brain undergo several changes with aging. One of the domains in which these changes are more remarkable relates with cognitive performance. In the present work, electroencephalogram (EEG) markers (power spectral density and spectral coherence) of age-related cognitive decline were sought whilst the subjects performed the Wisconsin Card Sorting Test (WCST). Considering the expected age-related cognitive deficits, WCST was applied to young, mid-age and elderly participants, and the theta and alpha frequency bands were analyzed. From the results herein presented, higher theta and alpha power were found to be associated with a good performance in the WCST of younger subjects. Additionally, higher theta and alpha coherence were also associated with good performance and were shown to decline with age and a decrease in alpha peak frequency seems to be associated with aging. Additionally, inter-hemispheric long-range coherences and parietal theta power were identified as age-independent EEG correlates of cognitive performance. In summary, these data reveals age-dependent as well as age-independent EEG correlates of cognitive performance that contribute to the understanding of brain aging and related cognitive deficits.

Keywords: Aging; EEG rhythms; cognition.

Figure 1

(A) Electrodes arrangement used in EEG recording and electrode locations selected for four electrode pools; (B) electrode pools considered for power analysis: FL-frontal left; FR-frontal right; PL-parietal left; PR-parietal right; and (C) pool couplings considered for coherence analysis: FL-FR, FL-PL, FL-PR, FR-PR, FR-PL, and PL-PR.

Figure 2

(A) Scatter plot of all subjects included in the study according to age and z-score performance on WCST; inset histograms show an increasing tendency to a bimodal z-score distribution as age increases; (B) statistics for young, mid-age and elders groups; (C) statistics for good performers, medium performers and poor performers clusters.

Figure 3

Analysis of age effects on Power Spectral Density (PSD) of alpha and theta rhythms during baseline recordings; (A) alpha PSD is generally higher on young subjects than on middle-age and elders; (B) alpha PSD is inversely correlated with age in all four electrode pools; (C) theta PSD is higher on young rather than on elder subjects in all electrode pools, and higher than on middle-aged subjects on FL pool; (D) theta PSD is inversely correlated with age in all four electrode pools.

Figure 4

Analysis of Power Spectral Density (PSD) of alpha and theta rhythms with simultaneous WCST performance; (A) alpha PSD is generally higher on young subjects than on middle-age and elders, during WCST performance; (B) alpha PSD is inversely correlated with age in right hemisphere; (C) theta PSD is generally higher on young subjects rather than on elders and middle-age subjects; (D) theta PSD is inversely correlated with age in frontal regions; (E) Baseline-corrected theta power recorded simultaneously to WCST is higher for good than for poor performers on PL scalp region; (F) Baseline-corrected theta power on PL is directly correlated with performance success on WCST.

Figure 5

Analysis of Spectal Coherence of alpha and theta rhythms acquired simultaneously to WCST performance; (A) alpha coherence is higher for young rather than older subjects on FL-FR and FR-PR scalp regions; (B) alpha spectral coherence is inversely correlated with age both on FL-FR and FR-PR couplings; (C) theta coherence is higher for young rather than older subjects on frontal inter-hemispheric FL-FR, FR-PL and FR-PR couplings; (D) theta spectral coherence is inversely correlated with age on FL-FR, FR-PL and FR-PR couplings; (E) baseline-corrected PL-PR alpha coherence is higher for good than for poor performers; (F) baseline-corrected PL-PR alpha coherence is directly correlated with performance success on WCST.

Figure 6

Analysis of performance effects on Spectral Coherence of alpha and theta rhythms recorded during the WCST performance; (A) alpha coherence between FL and PR scalp regions is higher for good than for poor performers; (B) FL-PR coherence of alpha rhythm is directly correlated with z-score performance on WCST; (C) Theta coherence between frontal left and parietal right scalp regions is higher for good than for poor performers; FL-PR coherence is higher for medium than for poor performers; (D) Theta coherence between frontal left and parietal right is directly correlated with z-score performance on WCST.

Figure 7

Analysis of age effects on alpha and theta rhythms during baseline and WCST recordings for good performers sub-group; (A) subgroup of good performers n = 37; (B) absolute alpha PSD is inversely correlated with age during baseline recordings on good performers; (C) absolute theta PSD is inversely correlated with age during baseline recordings on good performers; (D) absolute alpha PSD is inversely correlated with age during WCST recordings on good performers; (E) absolute theta PSD is inversely correlated with age during WCST recordings on good performers; (F) absolute alpha coherence is inversely correlated with age during WCST recordings on good performers, namely between FL-FR and FR-PR scalp regions; (G) absolute theta coherence is inversely correlated with age during WCST recordings on good performers, namely between FL-FR, FR-PR and FR-PL scalp regions.

Figure 8

Analysis of performance effects on alpha and theta coherence during WCST and baseline-corrected recordings for elders’ sub-group; (A) subgroup of elderly subjects n = 15; (B) Baseline-corrected alpha coherence between PL-PR scalp locations is directly correlated with performance z-scores during WCST recordings on elderly subjects; (C) Absolute alpha coherence between FL-PR scalp locations is directly correlated with performance z-scores of WCST recordings on elderly subjects; (D) absolute theta coherence between FL-PR scalp locations is directly correlated with performance z-scores of WCST recordings on elderly subjects.

Figure 9

Analysis of age and performance effects on alpha peak frequency (APF) acquired simultaneously to WCST performance; (A) APF is higher for young than middle-age subjects overall four electrode pools and higher than APF of elders on FL and PL electrode pools; APF is higher for elders than middle-age subjects on FR and PR scalp regions; (B) APF is inversely correlated with age on FL and PL electrode pools; (C) difference between left and right APF is higher for good and medium performers than for poor performers on frontal scalp regions; (D) difference between left and right APF is directly correlated with performance z-scores on frontal and parietal scalp regions.