2.1 Biological Perspectives

Biological Factors in Mental Disorders

The biological perspective explains mental disorders by looking at what's happening inside the body: your genes, brain chemistry, brain structure, and how these all interact. This approach matters because it forms the basis for most medication-based treatments and helps explain why some people are more vulnerable to disorders than others.

Genetics in Mental Disorders

No single gene causes a mental disorder. Instead, genetic predisposition means you inherit a vulnerability that, combined with environmental factors, raises your risk. Researchers use several types of studies to untangle genetic influence:

• Family studies show that mental disorders appear at higher rates among biological relatives of affected individuals. The closer the genetic relationship, the higher the risk.
• Twin studies compare monozygotic (identical) twins, who share 100% of their DNA, with dizygotic (fraternal) twins, who share about 50%. When identical twins show higher concordance rates (both twins having the same disorder) than fraternal twins, that points to genetic influence.
• Adoption studies look at children raised apart from their biological parents. If an adopted child develops a disorder that their biological parent had, genetics likely played a role, since the child didn't share the parent's environment.

None of these studies prove genetics alone causes a disorder. They show that biology loads the gun, but environment often pulls the trigger.

Neurotransmitters and Abnormal Behavior

Neurotransmitters are chemical messengers that carry signals between neurons. When their levels are too high, too low, or when receptors don't respond to them properly, behavior and mood can shift in ways linked to specific disorders.

• Serotonin regulates mood, sleep, appetite, and aggression. Low serotonin activity is associated with depression, anxiety, and impulsive behavior.
• Dopamine plays a role in reward, motivation, and attention. Too much dopamine activity in certain brain pathways is linked to the positive symptoms of schizophrenia (hallucinations, delusions), while low dopamine is associated with ADHD and the motivational deficits in depression.
• Norepinephrine regulates arousal, alertness, and the stress response. Imbalances are associated with anxiety disorders and depression.
• GABA is the brain's main inhibitory neurotransmitter, calming neural activity. Low GABA activity is linked to anxiety disorders. Glutamate is the main excitatory neurotransmitter, and imbalances have been implicated in schizophrenia and mood disorders.

Keep in mind that "chemical imbalance" is a simplification. Neurotransmitter systems interact with each other, and the relationship between a neurotransmitter and a disorder is rarely as simple as "too much" or "too little."

Brain Structure and Mental Health

Neuroimaging techniques allow researchers to see structural and functional differences in the brains of people with mental disorders. The main tools include:

• MRI (magnetic resonance imaging) shows brain structure in detail
• PET (positron emission tomography) tracks brain activity by measuring blood flow or glucose use
• fMRI (functional MRI) shows which brain areas are active during specific tasks

Three brain regions come up repeatedly in abnormal psychology:

• Prefrontal cortex: handles executive functions like decision-making, planning, and emotional regulation. Reduced activity or volume here is linked to depression, anxiety, and several personality disorders.
• Amygdala: processes emotions, especially fear. Hyperactivity in the amygdala is associated with anxiety disorders and PTSD.
• Hippocampus: critical for memory formation and emotional regulation. Reduced hippocampal volume has been found in people with depression and chronic stress-related disorders. For example, studies have shown measurable hippocampal shrinkage in patients with major depressive disorder compared to healthy controls.

Enlarged ventricles (the fluid-filled spaces in the brain) are one of the most replicated structural findings in schizophrenia, suggesting a loss of surrounding brain tissue.

Principles of Psychopharmacology

Psychopharmacology is the study of how medications affect mental processes and behavior. These drugs work by targeting the neurotransmitter systems described above. The four major categories to know:

• Antidepressants: SSRIs (like fluoxetine/Prozac) block the reuptake of serotonin, keeping more of it available in the synapse. SNRIs target both serotonin and norepinephrine. Older tricyclics work similarly but affect more neurotransmitter systems, which is why they tend to have more side effects.
• Antipsychotics: Typical antipsychotics (first-generation) block dopamine receptors to reduce hallucinations and delusions. Atypical antipsychotics (second-generation) also affect serotonin receptors and tend to have fewer motor side effects.
• Mood stabilizers: Lithium is the classic treatment for bipolar disorder, stabilizing mood to prevent both manic and depressive episodes. Certain anticonvulsants (like valproate) also serve as mood stabilizers.
• Anxiolytics: Benzodiazepines (like diazepam/Valium) enhance the effect of GABA, producing a calming effect quickly but carrying a risk of dependence. Buspirone modulates serotonin receptors and works more gradually without the same dependence risk.

Medications manage symptoms rather than cure disorders. They're most effective when combined with psychological treatment.

Neuroplasticity and Mental Health

Gene-Environment Interactions

Genes don't operate in a vacuum. Epigenetic modifications are changes in gene expression that happen without altering the DNA sequence itself. Environmental factors like chronic stress, trauma, or early childhood experiences can switch genes "on" or "off," affecting vulnerability to mental disorders.

Most mental disorders follow a polygenic pattern, meaning many genes each contribute a small effect. No single gene is responsible. The cumulative impact of dozens or even hundreds of gene variants, combined with environmental triggers, shapes overall risk. This is why predicting mental illness from genetics alone remains so difficult.

Brain Plasticity, Stress, and Development

Neuroplasticity refers to the brain's ability to reorganize itself by forming new neural connections throughout life. This concept is central to both how disorders develop and how treatment works. Therapy, for instance, can produce measurable changes in brain structure and function over time.

Chronic stress is one of the clearest examples of how experience reshapes the brain. Prolonged exposure to stress hormones (especially cortisol) can cause:

• Shrinkage in the hippocampus, impairing memory and emotional regulation
• Hyperactivation of the amygdala, heightening fear and anxiety responses
• Reduced functioning in the prefrontal cortex, weakening impulse control and decision-making

These stress-induced changes are associated with depression, anxiety disorders, and PTSD.

Two other categories of disorders highlight the role of brain biology across the lifespan:

• Neurodevelopmental disorders (such as autism spectrum disorder and ADHD) involve abnormalities in how the brain develops, with differences in structure and connectivity present from early life.
• Neurodegenerative disorders (such as Alzheimer's disease and Parkinson's disease) involve progressive loss of neurons and cognitive decline, typically later in life.