If amino acid neurotransmitters set the basic tone of brain activity, biogenic amines shape its nuance. This chapter explores the neurotransmitter systems that modulate how we feel, think, and act - particularly dopamine, serotonin, and noradrenaline. In this episode, we examine how these systems do not simply transmit signals, but regulate them. They influence mood, reward, motivation, attention, arousal, and stress responses - acting as global tuning systems that adjust the brain’s overall state. We explore dopamine as a mediator of salience and reward prediction, serotonin as a regulator of mood and emotional stability, and noradrenaline as a driver of alertness and adaptive response to challenge. These systems are widely projecting, originating in small brainstem nuclei but influencing vast cortical and subcortical networks. Crucially, dysfunction in these modulatory systems does not produce isolated symptoms, but shifts in how the brain interprets and responds to the world. Depression, anxiety, psychosis, and addiction can all be understood, in part, as alterations in these tuning mechanisms. This chapter provides a bridge between biology and experience - showing how subtle changes in neurochemistry can reshape perception, motivation, and meaning itself. Key Takeaways * Biogenic amines (dopamine, serotonin, noradrenaline) modulate brain function rather than directly drive signalling. * These systems influence mood, motivation, attention, arousal, and stress responses. * Dopamine is central to reward, salience, and prediction error. * Serotonin regulates mood, emotional balance, and behavioural inhibition. * Noradrenaline governs alertness, vigilance, and response to stress. * These neurotransmitters originate in small nuclei but project widely across the brain. * Dysregulation leads to shifts in perception and behaviour rather than isolated deficits. * Many psychiatric treatments target these systems to restore functional balance. This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit drmanaankarray.substack.com/subscribe