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Neuroimage. 2016 Mar;128:302-315. doi: 10.1016/j.neuroimage.2015.12.057. Epub 2016 Jan 11.

The inhibition/excitation ratio related to task-induced oscillatory modulations during a working memory task: A multtimodal-imaging study using MEG and MRS.

Author information

1
Department of Psychiatry and Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan. Electronic address: tyuichi@gunma-u.ac.jp.
2
Department of Psychiatry and Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
3
Kyushu University, Graduate School of Medicine, Department of Clinical Neurophysiology, Higashiku, Fukuoka, Japan.
4
Douglas Mental Health University Institute and Department of Psychiatry, McGill University, Montreal, QC, Canada.
5
Gunma University Faculty of Medicine, Maebashi, Gunma, Japan.
6
Department of Diagnostic Radiology and Nuclear Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.

Abstract

Detailed studies on the association between neural oscillations and the neurotransmitters gamma-aminobutyric acid (GABA) and glutamate have been performed in vitro. In addition, recent functional magnetic resonance imaging studies have characterized these neurotransmitters in task-induced deactivation processes during a working memory (WM) task. However, few studies have investigated the relationship between these neurotransmitters and task-induced oscillatory changes in the human brain. Here, using combined magnetoencephalography (MEG) and magnetic resonance spectroscopy (MRS), we investigated the modulation of GABA and glutamate + glutamine (Glx) concentrations related to task-induced oscillations in neural activity during a WM task. We first acquired resting-state MRS and MEG data from 20 healthy male volunteers using the n-back task. Time-frequency analysis was employed to determine the power induced during the encoding and retention phases in perigenual anterior cingulate cortex (pg-ACC), mid-ACC, and occipital cortex (OC). Statistical analysis showed that increased WM load was associated with task-induced oscillatory modulations (TIOMs) of the theta-gamma band relative to the zero-back condition (TIOM0B) in each volume of interest during the encoding phase of the n-back task. The task-induced oscillatory modulations in the two-back condition relative to the zero-back condition (TIOM2B-0B) were negatively correlated with the percent rate change of the correct hit rate for 2B-0B, but positively correlated with GABA/Glx. The positive correlation between TIOM2B-0B and GABA/Glx during the WM task indicates the importance of the inhibition/excitation ratio. In particular, a low inhibition/excitation ratio is essential for the efficient inhibition of irrelevant neural activity, thus producing precise task performance.

KEYWORDS:

Gamma-aminobutyric acid; Glutamate; Inhibition/excitation ratio; Magnetic resonance spectroscopy; Magnetoencephalography; Task-induced deactivation

[Indexed for MEDLINE]

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