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Spontaneous Alpha and Theta Oscillations Are Related to Complementary Aspects of Cognitive Control in Younger and Older Adults

ABSTRACT: The resting-state human electroencephalogram (EEG) power spectrum is dominated by alpha (8–12 Hz) and theta (4–8 Hz) oscillations, and also includes non-oscillatory broadband activity inversely related to frequency (1/f activity). Gratton proposed that alpha and theta oscillations are both related to cognitive control function, though in a complementary manner. Alpha activity is hypothesized to facilitate the maintenance of representations, such as task sets in preparation for expected task conditions. In contrast, theta activity would facilitate changes in representations, such as the updating of task sets in response to unpredicted task demands. Therefore, theta should be related to reactive control (which may prompt changes in task representations), while alpha may be more relevant to proactive control (which implies the maintenance of current task representations). Less is known about the possible relationship between 1/f activity and cognitive control, which was analyzed here in an exploratory fashion. To investigate these hypothesized relationships, we recorded eyes-open and eyes-closed resting-state EEG from younger and older adults and subsequently tested their performance on a cued flanker task, expected to elicit both proactive and reactive control processes. Results showed that alpha power and 1/f offset were smaller in older than younger adults, whereas theta power did not show age-related reductions. Resting alpha power and 1/f offset were associated with proactive control processes, whereas theta power was related to reactive control as measured by the cued flanker task. All associations were present over and above the effect of age, suggesting that these resting-state EEG correlates could be indicative of trait-like individual differences in cognitive control performance, which may be already evident in younger adults, and are still similarly present in healthy older adults.

SUBMITTER: Clements G

PROVIDER: S-EPMC8025241 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Theta oscillations (4-8 Hz) provide an organizing principle of cognitive control, allowing goal-directed behavior. In adults, theta power over medial-frontal cortex (MFC) underlies conflict/error monitoring, whereas theta connectivity between MFC and lateral-frontal regions reflects cognitive control recruitment. However, prior work has not separated theta responses that occur before and immediately after a motor response, nor explained how medial-lateral connectivity drives different kinds of control behaviors. Theta's role during adolescence, a developmental window characterized by a motivation-control mismatch also remains unclear. As social observation is known to influence motivation, this might be a particularly important context for studying adolescent theta dynamics. Here, adolescents performed a flanker task alone or under social observation. Focusing first on the nonsocial context, we parsed cognitive control into dissociable subprocesses, illustrating how theta indexes distinct components of cognitive control working together dynamically to produce goal-directed behavior. We separated theta power immediately before/after motor responses, identifying behavioral links to conflict monitoring and error monitoring, respectively. MFC connectivity was separated before/after responses and behaviorally-linked to reactive and proactive control, respectively. Finally, distinct forms of post-error control were dissociated, based on connectivity with rostral/caudal frontal cortex. Social observation was found to exclusively upregulate theta measures indexing post-response error monitoring and proactive control, as opposed to conflict monitoring and reactive control. Linking adolescent cognitive control to theta oscillations provides a bridge between non-invasive recordings in humans and mechanistic studies of neural oscillations in animal models; links to social observation provide insight into the motivation-control interactions that occur during adolescence.

Project description:ObjectivesCognitive load (CL) impairs listeners' ability to comprehend sentences, recognize words, and identify speech sounds. Recent findings suggest that this effect originates in a disruption of low-level perception of acoustic details. Here, we attempted to quantify such a disruption by measuring the effect of CL (a two-back task) on pure-tone audiometry (PTA) thresholds. We also asked whether the effect of CL on PTA was greater in older adults, on account of their reduced ability to divide cognitive resources between simultaneous tasks. To specify the mechanisms and representations underlying the interface between auditory and cognitive processes, we contrasted CL requiring visual encoding with CL requiring auditory encoding. Finally, the link between the cost of performing PTA under CL, working memory, and speech-in-noise (SiN) perception was investigated and compared between younger and older participants.DesignYounger and older adults (44 in each group) did a PTA test at 0.5, 1, 2, and 4 kHz pure tones under CL and no CL. CL consisted of a visual two-back task running throughout the PTA test. The two-back task involved either visual encoding of the stimuli (meaningless images) or subvocal auditory encoding (a rhyme task on written nonwords). Participants also underwent a battery of SiN tests and a working memory test (letter number sequencing).ResultsYounger adults showed elevated PTA thresholds under CL, but only when CL involved subvocal auditory encoding. CL had no effect when it involved purely visual encoding. In contrast, older adults showed elevated thresholds under both types of CL. When present, the PTA CL cost was broadly comparable in younger and older adults (approximately 2 dB HL). The magnitude of PTA CL cost did not correlate significantly with SiN perception or working memory in either age group. In contrast, PTA alone showed strong links to both SiN and letter number sequencing in older adults.ConclusionsThe results show that CL can exert its effect at the level of hearing sensitivity. However, in younger adults, this effect is only found when CL involves auditory mental representations. When CL involves visual representations, it has virtually no impact on hearing thresholds. In older adults, interference is found in both conditions. The results suggest that hearing progresses from engaging primarily modality-specific cognition in early adulthood to engaging cognition in a more undifferentiated way in older age. Moreover, hearing thresholds measured under CL did not predict SiN perception more accurately than standard PTA thresholds.

Project description:Meditation training is proposed to enhance mental well-being by modulating neural activity, particularly alpha and theta brain oscillations, and autonomic activity. Although such enhancement also depends on the quality of meditation, little is known about how these neural and physiological changes relate to meditation quality. One model characterizes meditation quality as five increasing levels of 'depth': hindrances, relaxation, concentration, transpersonal qualities and nonduality. We investigated the neural oscillatory (theta, alpha, beta and gamma) and physiological (respiration rate, heart rate and heart rate variability) correlates of the self-reported meditation depth in long-term meditators (LTMs) and meditation-naïve controls (CTLs). To determine the neural and physiological correlates of meditation depth, we modelled the change in the slope of the relationship between self-reported experiential degree at each of the five depth levels and the multiple neural and physiological measures. CTLs reported experiencing more 'hindrances' than LTMs, while LTMs reported more 'transpersonal qualities' and 'nonduality' compared to CTLs, confirming the experiential manipulation of meditation depth. We found that in both groups, theta (4-6 Hz) and alpha (7-13 Hz) oscillations were related to meditation depth in a precisely opposite manner. The theta amplitude positively correlated with 'hindrances' and increasingly negatively correlated with increasing meditation depth levels. Alpha amplitude negatively correlated with 'hindrances' and increasingly positively with increasing depth levels. The increase in the inverse association between theta and meditation depth occurred over different scalp locations in the two groups-frontal midline in LTMs and frontal lateral in CTLs-possibly reflecting the downregulation of two different aspects of executive processing-monitoring and attention regulation, respectively-during deep meditation. These results suggest a functional dissociation of the two classical neural signatures of meditation training, namely, alpha and theta oscillations. Moreover, while essential for overcoming 'hindrances', executive neural processing appears to be downregulated during deeper meditation experiences.

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Spontaneous Alpha and Theta Oscillations Are Related to Complementary Aspects of Cognitive Control in Younger and Older Adults

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