Chapter 17: Neural Dysfunctions, Mental Illness, and Drugs That Affect the Brain

The chapter integrates genetic predisposition, environmental stressors, and neurochemical dysfunction as interconnected factors that precipitate psychiatric disorders. A central focus examines how imbalances in monoamine neurotransmitters including serotonin, dopamine, and norepinephrine contribute to depression, though the chapter emphasizes that low neurotransmitter levels alone provide an incomplete explanation of depressive pathology. The discussion of schizophrenia addresses dopaminergic hyperactivity in mesolimbic pathways and how excessive D2 receptor signaling relates to positive symptoms such as hallucinations and delusions. Obsessive-compulsive disorder is presented through the lens of dysregulated cortico-striatal-thalamic circuits where serotonergic dysfunction perpetuates intrusive cognitions and compulsive behaviors. The chapter details how selective serotonin reuptake inhibitors increase synaptic serotonin availability, how antipsychotic medications antagonize dopamine receptors, and how anticonvulsant drugs modulate ion channels and excitatory neurotransmission. Epilepsy is examined as a condition of pathological neural synchronization where excessive excitatory activity triggers seizures, and anticonvulsants stabilize neuronal excitability thresholds. The chapter also covers non-pharmacological interventions including electroconvulsive therapy for treatment-resistant depression and deep brain stimulation for severe psychiatric and neurological conditions, explaining their mechanisms despite limited understanding of how therapeutic benefit emerges. Finally, the chapter considers how psychoactive substances including MDMA, classical hallucinogens, and cannabinoids alter consciousness and emotional processing by modulating multiple neurotransmitter systems, and discusses implications for understanding brain function and potential therapeutic applications.