Regionally specific human GABA concentration correlates with tactile discrimination thresholds

Abstract

The neural mechanisms underlying variability in human sensory perception remain incompletely understood. In particular, few studies have attempted to investigate the relationship between in vivo measurements of neurochemistry and individuals' behavioral performance. Our previous work found a relationship between GABA concentration in the visual cortex and orientation discrimination thresholds (Edden et al., 2009). In the present study, we used magnetic resonance spectroscopy of GABA and psychophysical testing of vibrotactile frequency thresholds to investigate whether individual differences in tactile frequency discrimination performance are correlated with GABA concentration in sensorimotor cortex. Behaviorally, individuals showed a wide range of discrimination thresholds ranging from 3 to 7.6 Hz around the 25 Hz standard. These frequency discrimination thresholds were significantly correlated with GABA concentration (r = -0.58; p < 0.05) in individuals' sensorimotor cortex, but not with GABA concentration in an occipital control region (r = -0.04). These results demonstrate a link between GABA concentration and frequency discrimination in vivo, and support the hypothesis that GABAergic mechanisms have an important role to play in sensory discrimination.

Figure 1.

Frequency discrimination paradigm. Frequency discrimination thresholds to a 25 Hz stimulus were determined for frequencies higher and lower than 25 Hz in a 2AFC paradigm. The order of presentation of the standard (25 Hz) and comparison stimuli were randomized.

Figure 2.

Voxel locations and spectra. a, A single-participant example voxel over the right sensorimotor cortex. The center of the voxel is placed on the “hand knob,” an anatomical landmark indicating the hand area of the primary motor cortex, with the hand area of primary somatosensory cortex, directly posterior across the central sulcus, also included (Yousry et al., 1997). b, An example voxel over occipital cortex. c, d, High-quality spectra from all participants for the sensorimotor (SM) and occipital cortex (OCC) voxels respectively, with a clearly distinguishable GABA peak at 3 ppm for all participants.

Figure 3.

a, Individual GABA concentration in sensorimotor cortex correlates significantly with frequency discrimination threshold (r = −0.58, p < 0.05). b, GABA concentration in occipital cortex does not correlate with tactile frequency discrimination threshold (r = −0.04, NS). GABA concentrations are corrected for tissue volume (gray matter + white matter).