Subtraction artifacts and frequency (mis-)alignment in J-difference GABA editing.

PURPOSE: To compare the repeatability of γ-aminobutyric acid (GABA) measurements using J-difference editing, before and after spectral realignment-a technique which has previously been demonstrated to improve the quality of J-difference GABA spectra. MATERIALS AND METHODS: We performed in vivo measurements in three brain regions (occipital, sensorimotor, and dorsolateral prefrontal cortex [DLPFC]), and analyzed these using alternative alignment approaches to evaluate the impact of alignment on repeatability: "Independent alignment" (aligning each subspectrum independently) and "Pairwise alignment" (aligning each on and off subspectrum as a pair) were compared. RESULTS: Pairwise alignment improved the group mean coefficient of variation in all regions; 0.4% in occipital, 1.1% in sensorimotor, and 1.1% in DLPFC. Independent alignment resulted in subtraction artifacts in the majority of cases, and increased the coefficient of variation in the DLPFC by 9.4%. Simulations demonstrate that the GABA quantification error in datasets with high B0 drift, is 4.5% without alignment, but <1% with optimal alignment. CONCLUSION: Pairwise alignment improves the repeatability of GABA spectroscopy data. However, independently aligning all on and off subspectra can lead to artifacts and worse repeatability when compared with nonaligned data.

Dorsolateral prefrontal γ-aminobutyric acid in men predicts individual differences in rash impulsivity.

BACKGROUND: Impulsivity is a multifaceted personality construct associated with numerous psychiatric disorders. Recent research has characterized four facets of impulsivity: "urgency" (the tendency to act rashly especially in the context of distress or cravings); "lack of premeditation" (not envisaging the consequences of actions); "lack of perseverance" (not staying focused on a task); and "sensation seeking" (engaging in exciting activities). Urgency is particularly associated with clinical populations and problematic disinhibited behavior. METHODS: We used magnetic resonance spectroscopy to measure concentration of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) in the dorsolateral prefrontal cortex (DLPFC) in two cohorts of 12 and 13 participants. RESULTS: We find that variation in trait urgency in healthy men correlates with GABA concentration in the DLPFC. The result was replicated in an independent cohort. More GABA predicted lower urgency scores, consistent with a role in self-control for GABA-mediated inhibitory mechanisms in DLPFC. CONCLUSIONS: These findings help account for individual differences in self-control and thus clarify the relationship between GABA and a wide range of psychiatric disorders associated with impaired self-control.

Individual differences in subconscious motor control predicted by GABA concentration in SMA.

Subliminal visual stimuli affect motor planning, but the size of such effects differs greatly between individuals. Here, we investigated whether such variation may be related to neurochemical differences between people. Cortical responsiveness is expected to be lower under the influence of more of the main inhibitory neurotransmitter, GABA. Thus, we hypothesized that, if an individual has more GABA in the supplementary motor area (SMA)--a region previously associated with automatic motor control--this would result in smaller subliminal effects. We measured the reversed masked prime--or negative compatibility--effect, and found that it correlated strongly with GABA concentration, measured with magnetic resonance spectroscopy. This occurred specifically in the SMA region, and not in other regions from which spectroscopy measurements were taken. We replicated these results in an independent cohort: more GABA in the SMA region is reliably associated with smaller effect size. These findings suggest that, across individuals, the responsiveness of subconscious motor mechanisms is related to GABA concentration in the SMA.

More GABA, less distraction: a neurochemical predictor of motor decision speed.

People vary markedly in the efficiency with which they can resolve competitive action decisions, even simple ones such as shifting gaze to one stimulus rather than another. We found that an individual's ability to rapidly resolve such competition is predicted by the concentration of GABA, the main inhibitory neurotransmitter, in a region of frontal cortex that is relevant for eye movements, but not in a control region (occipital cortex).