Neurotransmitters are chemical messengers that transmit signals between neurons. Several neurotransmitter systems have particularly important roles in cognition. Dopamine modulates reward processing, motivation, working memory, and learning from feedback. Acetylcholine supports attention, memory encoding, and cortical plasticity. Norepinephrine regulates arousal, attention, and stress responses. Serotonin influences mood, impulse control, and decision-making. GABA and glutamate are the primary inhibitory and excitatory neurotransmitters, respectively, governing the balance of neural activity.
Dopamine and Cognition
Dopamine plays a central role in reward-based learning through prediction error signals (see Rescorla-Wagner Model) and in working memory maintenance through D1 receptor activation in the prefrontal cortex. The inverted-U relationship between dopamine levels and prefrontal function means both too little (Parkinson's disease) and too much (schizophrenia) dopamine impair cognition. This principle has implications for pharmacological cognitive enhancement and for understanding why stimulant medications (which increase dopamine) help ADHD symptoms.
Understanding neurotransmitter-cognition relationships has fueled interest in cognitive enhancement. Cholinesterase inhibitors (donepezil) modestly slow cognitive decline in Alzheimer's disease. Modafinil may enhance executive function in sleep-deprived individuals. Methylphenidate and amphetamine improve attention in ADHD. However, cognitive enhancement in healthy individuals is modest and often accompanied by trade-offs (improving one function at the expense of another), reflecting the evolved optimization of neurotransmitter levels.