Fronto-parietal Coupling Research Articles

Structuring of Abstract Working Memory Content by Fronto-parietal Synchrony in Primate Cortex

How is neuronal activity across distant brain regions orchestrated to allow multiple stimuli to be stored together in working memory, yet maintained separate for individual readout and protection from distractors? Using paired recordings in the prefrontal and parietal cortex of monkeys discriminating numbers of items (numerosities), we found that working memory content is structured by frequency-specific oscillatory synchrony. Parieto-frontal signaling in the beta band carried information about the most recent numerical input. Fronto-parietal coupling in the theta band differentiated between multiple memorized numerosities. Task-relevant and distracting stimuli were nested in spiking activity of single prefrontal neurons, but could be separated by reading out spikes at distinct phases of parietal theta oscillations. The strength of phase-locked, cross-regional memory coding predicted task performance. Frequency-specific communication channels in the fronto-parietal network could enable serial bottom-up and parallel top-down information transmission, providing an important mechanism to protect working memory from interference.

Optimized Gamma Synchronization Enhances Functional Binding of Fronto-Parietal Cortices in Mathematically Gifted Adolescents during Deductive Reasoning.

As enhanced fronto-parietal network has been suggested to support reasoning ability of math-gifted adolescents, the main goal of this EEG source analysis is to investigate the temporal binding of the gamma-band (30–60 Hz) synchronization between frontal and parietal cortices in adolescents with exceptional mathematical ability, including the functional connectivity of gamma neurocognitive network, the temporal dynamics of fronto-parietal network (phase-locking durations and network lability in time domain), and the self-organized criticality of synchronizing oscillation. Compared with the average-ability subjects, the math-gifted adolescents show a highly integrated fronto-parietal network due to distant gamma phase-locking oscillations, which is indicated by lower modularity of the global network topology, more “connector bridges” between the frontal and parietal cortices and less “connector hubs” in the sensorimotor cortex. The time domain analysis finds that, while maintaining more stable phase dynamics of the fronto-parietal coupling, the math-gifted adolescents are characterized by more extensive fronto-parietal connection reconfiguration. The results from sample fitting in the power-law model further find that the phase-locking durations in the math-gifted brain abides by a wider interval of the power-law distribution. This phase-lock distribution mechanism could represent a relatively optimized pattern for the functional binding of frontal–parietal network, which underlies stable fronto-parietal connectivity and increases flexibility of timely network reconfiguration.

Prefrontal and limbic resting state brain network functional connectivity differs between nicotine-dependent smokers and non-smoking controls

BackgroundBrain dysfunction in prefrontal cortex (PFC) and dorsal striatum (DS) contributes to habitual drug use. These regions are constituents of brain networks thought to be involved in drug addiction. To investigate whether networks containing these regions differ between nicotine dependent female smokers and age-matched female non-smokers, we employed functional MRI (fMRI) at rest. MethodsData were processed with independent component analysis (ICA) to identify resting state networks (RSNs). We identified a subcortical limbic network and three discrete PFC networks: a medial prefrontal cortex (mPFC) network and right and left lateralized fronto-parietal networks common to all subjects. We then compared these RSNs between smokers and non-smokers using a dual regression approach. ResultsSmokers had greater coupling versus non-smokers between left fronto-parietal and mPFC networks. Smokers with the greatest mPFC–left fronto-parietal coupling had the most DS smoking cue reactivity as measured during an fMRI smoking cue reactivity paradigm. This may be important because the DS plays a critical role in maintaining drug-cue associations. Furthermore, subcortical limbic network amplitude was greater in smokers. ConclusionsOur results suggest that prefrontal brain networks are more strongly coupled in smokers, which could facilitate drug-cue responding. Our data also are the first to document greater reward-related network fMRI amplitude in smokers. Our findings suggest that resting state PFC network interactions and limbic network amplitude can differentiate nicotine-dependent smokers from controls, and may serve as biomarkers for nicotine dependence severity and treatment efficacy.

Neural Mechanisms of Interference Control and Time Discrimination in Attention-Deficit/Hyperactivity Disorder

Both executive functions and time perception are typically impaired in subjects with attention-deficit/hyperactivity disorder (ADHD). However, the exact neural mechanisms underlying these deficits remain to be investigated. Fourteen subjects with ADHD and 14 age- and IQ-matched controls (aged 9 through 15 years) were assessed with functional magnetic resonance imaging while they performed a combined spatial stimulus-response compatibility (SRC) and time duration discrimination (TD) paradigm using identical stimuli for all experimental conditions. Children with ADHD performed less accurately in the SRC but not in the TD task compared with controls. On the brain level, subjects with ADHD showed significantly reduced neural activity in the left putamen during SRC and reduced fronto-cerebellar activation during TD when compared with the baseline conditions. Compared with subjects with ADHD, control subjects had increased activation in a left-hemispheric fronto-parietal network during the SRC task and in the right superior-frontal gyrus during the TD task. Functional connectivity analyses revealed abnormal fronto-parietal coupling during the SRC task and reduced fronto-cerebellar connectivity during the TD task in the ADHD group compared with controls. Our findings suggest specific but distinct patterns of cerebral dysfunction associated with interference control and TD processing in ADHD, characterized by both reduced neural activation in regions critical for task performance and reduced co-activation of frontal cortex. Group differences on the behavioral level were controlled by several methodological approaches. Nonetheless, given the use of a block design, we cannot rule out the possibility that between-group differences in behavior confounded the neural activation patterns.

Fronto-parietal coupling of brain rhythms in mild cognitive impairment: A multicentric EEG study

Electroencephalographic (EEG) data were recorded in 69 normal elderly (Nold), 88 mild cognitive impairment (MCI), and 109 mild Alzheimer's disease (AD) subjects at rest condition, to test whether the fronto-parietal coupling of EEG rhythms is in line with the hypothesis that MCI can be considered as a pre-clinical stage of the disease at group level. Functional coupling was estimated by synchronization likelihood of Laplacian-transformed EEG data at electrode pairs, which accounts for linear and non-linear components of that coupling. Cortical rhythms of interest were delta (2–4 Hz), theta (4–8 Hz), alpha 1 (8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), beta 2 (20–30 Hz), and gamma (30–40 Hz). Compared to the Nold subjects, the AD patients presented a marked reduction of the synchronization likelihood (delta to gamma) at both fronto-parietal and inter-hemispherical (delta to beta 2) electrodes. As a main result, alpha 1 synchronization likelihood progressively decreased across Nold, MCI, and mild AD subjects at midline (Fz–Pz) and right (F4–P4) fronto-parietal electrodes. The same was true for the delta synchronization likelihood at right fronto-parietal electrodes (F4–P4). For these EEG bands, the synchronization likelihood correlated with global cognitive status as measured by the Mini Mental State Evaluation. The present results suggest that at group level, fronto-parietal coupling of the delta and alpha rhythms progressively becomes abnormal though MCI and mild AD. Future longitudinal research should evaluate whether the present EEG approach is able to predict the cognitive decline in individual MCI subjects.

Functional frontoparietal connectivity during encoding and retrieval processes follows HERA model: A high-resolution study

Recent neuroimaging studies of long-term episodic memory have suggested that left prefrontal cortex predominates in encoding condition, whereas right prefrontal cortex predominates in retrieval condition (hemispheric encoding and retrieval asymmetry, HERA model). The present electroencephalographic (EEG) study investigated the functional coupling of fronto-parietal regions during long-term memorization of visuo-spatial contents (i.e. landscapes, interiors of apartments), to test the predictions of the HERA model. Global fronto-parietal coupling was estimated by spectral coherence, whereas the “direction” of the fronto-parietal information flow was estimated by directed transfer function (DTF). The EEG rhythms of interest were theta (4–7 Hz), alpha (8–13 Hz), beta (14–30 Hz), and gamma (30–45 Hz). Statistically significant coherence in line with the HERA model was obtained at the gamma band. Namely, the fronto-parietal gamma coherence prevailed in the left hemisphere during the encoding condition and in the right hemisphere during the retrieval condition. The DTF estimates of the gamma band showed a dominant parietal-to-frontal directional flow in the right hemisphere during the encoding condition and in the left hemisphere during the retrieval condition (i.e. hemisphere-condition combination not involved by the HERA model). In contrast, a balanced bidirectional flow of the fronto-parietal coupling was observed in the left hemisphere during the encoding condition and in the right hemisphere during the retrieval condition (i.e. hemisphere-condition combination involved by the HERA model). In conclusion, the present encoding-retrieval conditions induced maximal fronto-parietal gamma coupling with bidirectional information flow in the hemisphere-condition combination predicted by the HERA model.

The functional states of the thalamus and the associated neuronal interplay.

The functional states of the thalamus and the associated neuronal interplay.