http://www.cognitiveneuroscience.it/wp-content/uploads/2015/10/Rossini_CliNeuro_2015.pdf

Non-invasive electrical and magnetic stimulation of the brain, spinal cord, roots and peripheral nerves: Basic principles and procedures for routine clinical and research application: An updated report from an I.F.C.N. Committee

http://godzilla.kennedykrieger.org/~raee2/YNIMG_10001.pdf

Current practice in the use of MEGA-PRESS spectroscopy for the detection of GABA

http://www.tmslab.org/tdcs%20articles/006.pdf

Applications of transcranial direct current stimulation for understanding brain function

The current knowledge of the normal biochemistry of compounds that give rise to resonances in human brain proton magnetic resonance spectra measureable at readily available field strengths (i.e. ≤3 T) is reviewed. Molecules covered include myo- and scyllo-inositol, glycerophospho- and phospho-choline and choline, creatine and phosphocreatine, N-acetylaspartate, N-acetylaspartylglutamate, glutamate, glutamine, γ-aminobutyrate, glucose, glutathione and lactate. The factors which influence changes in the levels of these compounds are discussed. As most proton resonances in the brain at low field are derived from a combination of moieties whose biochemistry is complex and interrelated, an understanding of the mechanisms underlying why these species change is crucial to meaningful interpretation of human brain spectra.

A Guide to the Metabolic Pathways and Function of Metabolites Observed in Human Brain 1H Magnetic Resonance Spectra

GABA system dysfunction in autism and related disorders: from synapse to symptoms.

Magnetic resonance spectroscopy (MRS) allows measurement of neurotransmitter concentrations within a region of interest in the brain. Inter-individual variation in MRS-measured GABA levels have been related to variation in task performance in a number of regions. However, it is not clear how MRS-assessed measures of GABA relate to cortical excitability or GABAergic synaptic activity. We therefore performed two studies investigating the relationship between neurotransmitter levels as assessed by MRS and transcranial magnetic stimulation (TMS) measures of cortical excitability and GABA synaptic activity in the primary motor cortex. We present uncorrected correlations, where the P value should therefore be considered with caution. We demonstrated a correlation between cortical excitability, as assessed by the slope of the TMS input-output curve and MRS-assessed glutamate levels (r = 0.803, P = 0.015) but no clear relationship between MRS-assessed GABA levels and TMS-assessed synaptic GABA(A) activity (2.5 ms inter-stimulus interval (ISI) short-interval intracortical inhibition (SICI); Experiment 1: r = 0.33, P = 0.31; Experiment 2: r = -0.23, P = 0.46) or GABA(B) activity (long-interval intracortical inhibition (LICI); Experiment 1: r = -0.47, P = 0.51; Experiment 2: r = 0.23, P = 0.47). We demonstrated a significant correlation between MRS-assessed GABA levels and an inhibitory TMS protocol (1 ms ISI SICI) with distinct physiological underpinnings from the 2.5 ms ISI SICI (r = -0.79, P = 0.018). Interpretation of this finding is challenging as the mechanisms of 1 ms ISI SICI are not well understood, but we speculate that our results support the possibility that 1 ms ISI SICI reflects a distinct GABAergic inhibitory process, possibly that of extrasynaptic GABA tone.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.2011.216978

Relationship between physiological measures of excitability and levels of glutamate and GABA in the human motor cortex

A major cause of disability after stroke is impaired contralateral manual dexterity. Recently it has been suggested that this may be at least partly due to a maladaptive increase in inhibition from the unaffected primary motor cortex (M1). Transcranial direct current stimulation (tDCS) is a non-invasive potential therapy that modulations M1 excitability via a weak electrical direct current applied to the scalp. Immediate improvement of affected hand function was obtained by anodal (excitatory) tDCS over the affected M1 or by cathodal (inhibitory) tDCS over the unaffected M1. Although the tDCS “after-effects” can last for hours to days following a 20-minute stimulation session, they are inherently transitory. There is hope that repeated tDCS sessions applied early after stroke could reduce the maladaptive neuroplasiticy and aid hand dexterity rehabilitation.

A O Constantinescu

Papers

Relationship between physiological measures of excitability and levels of glutamate and GABA in the human motor cortex

Trans-cranial direct current stimulation (tDCS): A promising new tool to facilitate rehabilitation of manual dexterity after stroke