Age-related differences in transient gamma band activity during working memory maintenance through adolescence

Adolescent maturation of dorsolateral prefrontal cortex glutamate:GABA and cognitive function is supported by dopamine-related neurobiology

Developmental changes in prefrontal cortex (PFC) excitatory (glutamatergic, Glu) and inhibitory (gamma- aminobutryic acid, GABA) neurotransmitter balance (E:I) have been identified during human adolescence, potentially reflecting a critical period of plasticity that supports the maturation of PFC-dependent cognition. Animal models implicate increases in dopamine (DA) in regulating changes in PFC E:I during critical periods of development, however, mechanistic relationships between DA and E:I have not been studied in humans. Here, we used high field (7T) echo planar imaging (EPI) in combination with Magnetic Resonance Spectroscopic Imaging (MRSI) to assess the role of basal ganglia tissue iron-reflecting DA neurophysiology-in longitudinal trajectories of dorsolateral PFC Glu, GABA, and their relative levels (Glu:GABA) and working memory performance from adolescence to adulthood in 153 participants (ages 10-32 years old, 1-3 visits, 272 visits total). Using generalized additive mixed models (GAMMs) that capture linear and non-linear developmental processes, we show that basal ganglia tissue iron increases during adolescence, and Glu:GABA is biased towards heightened Glu relative to GABA early in adolescence, decreasing into adulthood. Critically, variation in basal ganglia tissue iron was linked to different age-related trajectories in Glu:GABA and working memory. Specifically, individuals with higher levels of tissue iron showed a greater degree of age-related declines in Glu and Glu:GABA, resulting in lower Glu relative to GABA (i.e., higher GABA relative to Glu) in young adulthood. Variation in tissue iron additionally moderated working memory trajectories, as higher levels of tissue iron were associated with steeper age-related improvements and better performance into adulthood. Our results provide novel evidence for a model of critical period plasticity whereby individual differences in DA may be involved in fine-tuning PFC E:I and PFC-dependent cognitive function at a critical transition from adolescence into adulthood.

Neurobehavioural Correlates of Breath Meditation in Novice Adolescents: Insights from Anapanasati-based Paradigm

Background

Breath-awareness practices contribute to stress management and psychological well-being among adolescents. However, their neurobehavioural effects remain underexplored, specifically in the Indian developmental context.

Purpose

This study examined how breath-based Ānāpānasati meditation affects brain electrical activity and the subjective self-reported experiences in adolescent novice meditators posteriori a cognitive workload-inducing task.

Methods

Anapanasati meditation was adapted into a three-stage breath-awareness intervention framework and was administered to 45 novice adolescent meditators. Brain activity was investigated through electroencephalography (EEG), and neural oscillations were measured over the three stages, namely resting state (RS), breath counting (BC) and breath focus (BF). Further, adolescents' breath awareness self-reports were evaluated employing the Amsterdam Resting-State Questionnaire (ARSQ) following the BF stage and the breath count feedback (BCF) after the BC stage. Both the inventories displayed satisfactory psychometric properties, thus facilitating a neurobehavioural analysis in a cross-sectional within-subjects setting.

Results

Alpha oscillation was significantly increased throughout the intervention, indicating relaxation. Beta power in both the occipital and midline default mode network (DMN) regions during the count and focus stages exhibited significant positive associations with breath count, suggesting enhanced visual and cognitive processing. Blissfulness felt during counting breaths was also associated with enhanced state mindfulness, sharing a notable negative association with the theory of mind (TOM). State mindfulness further correlated with increased frontal alpha activity, while the theory of mind negatively predicted frontal alpha power. Lastly, exploratory analysis revealed gender differences, with females demonstrating greater frontal beta activity and state mindfulness.

Conclusion

Breath-awareness meditation can thus be effective for promoting relaxation and blissfulness in adolescents, with possible gender-based variations influencing its impact. Moreover, the positive association of prefrontal alpha with self-reported state mindfulness and its negative association with TOM underscored an inverse interplay between inward-focused mindfulness and outward-directed social cognitive states in adolescents.

Dysfunctional oscillatory bursting patterns underlie working memory deficits in adolescents with ADHD

Identifying neural markers of clinical symptom fluctuations is prerequisite to developing more precise brain-targeted treatments in psychiatry. We have recently shown that working memory (WM) in healthy adults is dependent on the rise and fall interplay between alpha/beta and gamma bursts within frontoparietal regions, and that deviations in these patterns lead to WM performance errors. However, it is not known whether such bursting deviations underlie clinically relevant WM-related symptoms or clinical status in individuals with WM deficits. In adolescents (n=27) with attention deficit hyperactivity disorder (ADHD), we investigated WM-related dynamics between alpha/beta and gamma bursts in relation to clinical status fluctuations. Participants repeatedly completed a visual Sternberg spatial working memory task during EEG recording as part of their participation in two research studies (n=224 person-sessions). Source localizing EEG data to each participant's structural MRI, the rate and volume of alpha, beta, and gamma bursts were examined within the dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex (PPC). Alpha/beta and gamma bursts at the DLPFC and PPC displayed complimentary roles in WM processes. Alpha/beta bursting decreased during stimuli encoding and increased during the delay, while gamma bursting was elevated during encoding and decreased during the delay. Deviations in bursting patterns were associated with WM errors and clinical symptoms. We conclude that dysfunctional alpha/beta and gamma burst dynamics within the frontoparietal region underlie both intra-individual WM performance and WM symptom fluctuations in adolescents with ADHD. Such burst dynamics reflect a novel target and biomarker for WM-related treatment development.

Measuring neuroplasticity in human development: the potential to inform the type and timing of mental health interventions

Neuroplasticity during sensitive periods, the molecular and cellular process of enduring neural change in response to external stimuli during windows of high environmental sensitivity, is crucial for adaptation to expected environments and has implications for psychiatry. Animal research has characterized the developmental sequence and neurobiological mechanisms that govern neuroplasticity, yet gaps in our ability to measure neuroplasticity in humans limit the clinical translation of these principles. Here, we present a roadmap for the development and validation of neuroimaging and electrophysiology measures that index neuroplasticity to begin to address these gaps. We argue that validation of measures to track neuroplasticity in humans will elucidate the etiology of mental illness and inform the type and timing of mental health interventions to optimize effectiveness. We outline criteria for evaluating putative neuroimaging measures of plasticity in humans including links to neurobiological mechanisms shown to govern plasticity in animal models, developmental change that reflects heightened early life plasticity, and prediction of neural and/or behavior change. These criteria are applied to three putative measures of neuroplasticity using electroencephalography (gamma oscillations, aperiodic exponent of power/frequency) or functional magnetic resonance imaging (amplitude of low frequency fluctuations). We discuss the use of these markers in psychiatry, envision future uses for clinical and developmental translation, and suggest steps to address the limitations of the current putative neuroimaging measures of plasticity. With additional work, we expect these markers will significantly impact mental health and be used to characterize mechanisms, devise new interventions, and optimize developmental trajectories to reduce psychopathology risk.

Prefrontal Excitation/ Inhibition Balance Supports Adolescent Enhancements in Circuit Signal to Noise Ratio

The development and refinement of neuronal circuitry allow for stabilized and efficient neural recruitment, supporting adult-like behavioral performance. During adolescence, the maturation of PFC is proposed to be a critical period (CP) for executive function, driven by a break in balance between glutamatergic excitation and GABAergic inhibition (E/I) neurotransmission. During CPs, cortical circuitry fine-tunes to improve information processing and reliable responses to stimuli, shifting from spontaneous to evoked activity, enhancing the SNR, and promoting neural synchronization. Harnessing 7T MR spectroscopy and EEG in a longitudinal cohort (N = 164, ages 10-32 years, 283 neuroimaging sessions), we outline associations between age-related changes in glutamate and GABA neurotransmitters and EEG measures of cortical SNR. We find developmental decreases in spontaneous activity and increases in cortical SNR during our auditory steady state task using 40 Hz stimuli. Decreases in spontaneous activity were associated with glutamate levels in DLPFC, while increases in cortical SNR were associated with more balanced Glu and GABA levels. These changes were associated with improvements in working memory performance. This study provides evidence of CP plasticity in the human PFC during adolescence, leading to stabilized circuitry that allows for the optimal recruitment and integration of multisensory input, resulting in improved executive function.

Better with age: Developmental changes in oscillatory activity during verbal working memory encoding and maintenance

Numerous investigations have characterized the oscillatory dynamics serving working memory in adults, but few have probed its relationship with chronological age in developing youth. We recorded magnetoencephalography during a modified Sternberg verbal working memory task in 82 youth participants aged 6-14 years old. Significant oscillatory responses were identified and imaged using a beamforming approach and the resulting whole-brain maps were probed for developmental effects during the encoding and maintenance phases. Our results indicated robust oscillatory responses in the theta (4-7 Hz) and alpha (8-14 Hz) range, with older participants exhibiting stronger alpha oscillations in left-hemispheric language regions. Older participants also had greater occipital theta power during encoding. Interestingly, there were sex-by-age interaction effects in cerebellar cortices during encoding and in the right superior temporal region during maintenance. These results extend the existing literature on working memory development by showing strong associations between age and oscillatory dynamics across a distributed network. To our knowledge, these findings are the first to link chronological age to alpha and theta oscillatory responses serving working memory encoding and maintenance, both across and between male and female youth; they reveal robust developmental effects in crucial brain regions serving higher order functions.

Aperiodic EEG and 7T MRSI evidence for maturation of E/I balance supporting the development of working memory through adolescence

Adolescence has been hypothesized to be a critical period for the development of human association cortex and higher-order cognition. A defining feature of critical period development is a shift in the excitation: inhibition (E/I) balance of neural circuitry, however how changes in E/I may enhance cortical circuit function to support maturational improvements in cognitive capacities is not known. Harnessing ultra-high field 7 T MR spectroscopy and EEG in a large, longitudinal cohort of youth (N = 164, ages 10-32 years old, 347 neuroimaging sessions), we delineate biologically specific associations between age-related changes in excitatory glutamate and inhibitory GABA neurotransmitters and EEG-derived measures of aperiodic neural activity reflective of E/I balance in prefrontal association cortex. Specifically, we find that developmental increases in E/I balance reflected in glutamate:GABA balance are linked to changes in E/I balance assessed by the suppression of prefrontal aperiodic activity, which in turn facilitates robust improvements in working memory. These findings indicate a role for E/I-engendered changes in prefrontal signaling mechanisms in the maturation of cognitive maintenance. More broadly, this multi-modal imaging study provides evidence that human association cortex undergoes physiological changes consistent with critical period plasticity during adolescence.