Fig. 4.

Correlating γ-aminobutyric acid (GABA) change with behavioral improvement. a Skipped Pearson’s correlations showing a significant negative correlation of GABA/tCr change in occipito-temporal cortex with behavioral improvement for the signal-in-noise task (n = 16, r = -0.43, CI = [–0.75, –0.002]), whereas a significant positive correlation for the feature differences task (n = 19, r = 0.55, CI = [0.10, 0.78]). We computed GABA/tCr change for each participant as the difference between GABA/tCr in the training block with maximum performance and GABA/tCr in the baseline block. Note that the temporal resolution of GABA measurements does not allow us to separate the different processes associated with different events in a trial (e.g., stimulus vs. response). Thus, the correlations we report here relate learning-dependent changes in GABA levels to learning-dependent changes in overall task performance. The plots indicate that for a small number of participants the data deviated from the overall pattern of the correlation; e.g., for some participants in the SD task, GABA/tCr values were higher rather than lower compared with baseline. Our treatment of the data (i.e., GABA data are expressed as percent over baseline; behavioral improvement is expressed as percent over early performance) accounts for potential differences across participants in performance early in training or baseline GABA before training. It is possible that this individual variability was due to the single training session employed in our study during which participant performance did not saturate (i.e., average 72% maximum performance across participants). b Correlations of posterior parietal GABA/tCr change from baseline with behavioral improvement were not significant for the signal-in-noise (n = 17, r = –0.23, CI = [–0.61, 0.19]) or the feature differences task (n = 21, r = 0.05, CI = [–0.37, 0.43]). Significant correlations are indicated by closed symbols; nonsignificant correlations by open symbols