GABA levels and measures of intracortical and interhemispheric excitability in healthy young and older adults: an MRS-TMS study

Neurobiol Aging. 2018 May;65:168-177. doi: 10.1016/j.neurobiolaging.2018.01.023. Epub 2018 Feb 6.

Abstract

Edited magnetic resonance spectroscopy (MRS) and transcranial magnetic stimulation (TMS) have often been used to study the integrity of the GABAergic neurotransmission system in healthy aging. To investigate whether the measurement outcomes obtained with these 2 techniques are associated with each other in older human adults, gamma-aminobutyric acid (GABA) levels in the left sensorimotor cortex were assessed with edited MRS in 28 older (63-74 years) and 28 young adults (19-34 years). TMS at rest was then used to measure intracortical inhibition (short-interval intracortical inhibition/long-interval intracortical inhibition), intracortical facilitation, interhemispheric inhibition from left to right primary motor cortex (M1) and recruitment curves of left and right M1. Our observations showed that short-interval intracortical inhibition and long-interval intracortical inhibition in the left M1 were reduced in older adults, while GABA levels did not significantly differ between age groups. Furthermore, MRS-assessed GABA within left sensorimotor cortex was not correlated with TMS-assessed cortical excitability or inhibition. These observations suggest that healthy aging gives rise to altered inhibition at the postsynaptic receptor level, which does not seem to be associated with MRS-assessed GABA+ levels.

Keywords: Aging; Gamma-aminobutyric acid (GABA); Interhemispheric inhibition; Intracortical inhibition; Magnetic resonance spectroscopy (MRS); Transcranial magnetic stimulation (TMS).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Cortical Excitability / physiology*
  • Female
  • Healthy Aging / metabolism*
  • Healthy Aging / physiology*
  • Healthy Volunteers*
  • Humans
  • Magnetic Resonance Spectroscopy
  • Motor Cortex / physiology
  • Neural Inhibition / physiology
  • Rest / physiology
  • Sensorimotor Cortex / metabolism*
  • Sensorimotor Cortex / physiology*
  • Synaptic Transmission
  • Transcranial Magnetic Stimulation
  • Young Adult
  • gamma-Aminobutyric Acid / metabolism*
  • gamma-Aminobutyric Acid / physiology

Substances

  • gamma-Aminobutyric Acid