Distinct neurochemical predictors for different phases of decision-making learning.

Fast and accurate sensory-motor mapping is characteristic of successful interaction with our environment and decision-making. Learning is crucial for the development of decision-making processes and has been linked to the balance of excitatory (glutamate) and inhibitory (γ-aminobutyric acid [GABA]) neurochemicals in the cortex. However, learning is not a unitary phenomenon and occurs across time. How neurochemical concentrations are involved, and the role of interventions like transcranial direct current stimulation (tDCS) remains unclear. The efficacy of tDCS to modulate learning has been linked to baseline concentrations of GABA and glutamate, and stimulation may influence neurochemical concentrations. Here, we assessed how neurochemical balance is associated with tDCS modulations to early- and later-phase sensory-motor learning using in vivo 7T ultra-high field magnetic resonance spectroscopy of the right motor cortex (M1), right intraparietal sulcus (IPS), and left prefrontal cortex. A single-dual task paradigm assessed performance immediately post (early learning) and 20 min post (later learning) offline cathodal stimulation to the left prefrontal cortex. tDCS modulations to learning were associated with neurochemical balance in right IPS during early learning, which shifted to right M1 for later learning. These findings elucidate the neurochemical mechanisms at play as sensory-response mappings shift from executive to motoric operations.