A Primer on Biological Psychology, Explained

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A Primer on Biological Psychology

Abnormal Psychology · Chapter 3: Biological Underpinnings of Psychological DisordersSection 3.1 · lesson 9 of 9717 min · free with a free account

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In this lesson

How physical factors contribute - and why contribution is not determination.

  • State what the biological model claims, and how far it reaches
  • Describe the nested levels at which biological explanation operates
  • Explain why a biological correlate is not a biological cause
  • Say why medical rule-out precedes psychiatric attribution

Transcript

Everything said in the video, section by section (2,326 words). Read along, or search it.

Biological Underpinnings of Psychological Disorders

A Primer on Biological Psychology

Chapter three is the biological chapter, and this section sets its terms. What the biological model claims, and how far the claim actually reaches. The levels at which biological explanation operates, from molecules to the whole body. The physical states that can produce, worsen, or imitate psychological symptoms. Why a clinician checks the thyroid before settling a diagnosis of depression. Then the sentence you should carry out of the whole chapter. A biological correlate is not a biological cause. We look at four alternatives that stay open on every brain-imaging finding. And we take the strongest objection to the whole model seriously. Not the weak version. The version its defenders find hard to answer.

Before You Begin

Contribution Is Not Determination

Two notes before we begin, and the second one governs everything after it. This material is educational. It is not a basis for diagnosing anyone. Nor for interpreting anyone's medical results, including your own. Every case described here is a composite that describes no real person. Now the governing point. Showing that biology contributes to a condition is not showing that biology determines it. And finding a biological correlate is not finding a biological cause. Nothing here implies that a person has less agency because biology is involved. Or less responsibility for their choices, or a worse outlook. The opposite is closer to the truth. Biological understanding has produced treatments that improve outcomes.

The Core Claim

A Claim About Implementation, Not Importance

The biological model holds that psychological conditions arise from the workings of the body. And that they are expressed through those workings. Principally the nervous system, and also the endocrine, immune, and metabolic systems. Stated carefully, the claim has three parts. Every psychological state has a physical implementation. Differences in psychological state correspond to differences in that implementation. And intervening on the physical system can therefore change the psychological state. Now notice how much that claim does not include. It does not say biology is the only relevant level of explanation. It does not say biological factors are the most important ones. And it does not say psychological and social factors are secondary. A person can accept the whole of that claim, and still hold something else. That the most useful account of a particular condition is about circumstances. Circumstances rather than chemistry. The claim is about implementation, not importance.

Levels

Five Nested Scales, None of Them Competing

Biological explanation is not one thing. It operates at several levels of analysis. Scales at which a system can be described, each with its own questions and methods. And each with its own characteristic errors. The levels are nested. The molecular sits inside the cellular. The cellular sits inside circuits, and circuits sit inside the whole brain. And the whole brain sits inside the whole body. At the molecular level you might ask whether a receptor becomes less responsive. Less responsive after prolonged exposure to a molecule. At the cellular level, how an electrical signal travels along a nerve cell. At the circuit level, which pathway carries information from a threat-detection structure. To the regions that regulate it, that is. At the whole-brain level, whether connectivity during a task differs between groups. And at the whole-body level, whether inflammation elsewhere accompanies changes in mood. Two mistakes follow from ignoring the levels. The first is answering a question at the wrong level. Asking about molecules when the question concerns circuits. The second is more serious, and more common. Assuming that an explanation at a lower level replaces one at a higher level. It does not. Those are answers to different questions.

Organization

The Nervous System, and the Endocrine System Beside It

The nervous system is the network of cells that receives, integrates, and transmits. It divides into two parts, and then keeps dividing. The central nervous system is the brain and the spinal cord. That is where integration and decision take place. The peripheral nervous system is every nerve outside those two structures. It carries information inward from the body, and instructions outward to it. The peripheral system divides again. The somatic system handles voluntary movement, and sensation from skin, muscles, and joints. The autonomic system regulates organs, glands, and vessels automatically. Largely outside awareness. And the autonomic system divides once more, into the division that matters most here. The sympathetic branch mobilizes the body for action. Raising heart rate and breathing, diverting blood to the muscles, sharpening attention. The parasympathetic branch restores the body afterward. Slowing the heart, supporting digestion and recovery. Now notice why that matters clinically. The physical experience of intense anxiety is largely sympathetic activation. Racing heart, rapid breathing, tightness, trembling. Explaining that branch to a person having panic symptoms is itself an intervention. Alongside all of this runs the endocrine system. Glands releasing hormones into the bloodstream, to act on distant organs. The two systems interface directly, and the traffic runs in both directions. Which is why a hormonal condition can present as a psychological one.

Cells

Neurons, and the Cells That Outnumber Them

A neuron is a cell specialized for receiving, integrating, and transmitting signals. Four parts are worth naming. The dendrites are branching extensions that receive signals from other cells. The cell body integrates those signals, and keeps the cell alive. The axon is a single long projection carrying the outgoing signal. And the terminal at the axon's end is where the signal is passed on. Now the part that matters for the rest of the chapter. Signals travel within a neuron electrically, and pass between neurons chemically. They pass at a junction called the synapse. The narrow gap across which one neuron communicates with the next. What happens at that synapse is the whole subject of the next section. Neurons are outnumbered in the brain by glial cells. Supporting cells that maintain the conditions neurons need in order to work. They were long treated as packing material, and they do considerably more. They form the insulating sheath that speeds signal conduction. They regulate the chemical environment around synapses, and supply nutrients. They clear debris, and take part in immune responses within the brain. But describe their role accurately. Their part in psychological conditions is an active research question, not a settled account.

Physical Contributors

States That Produce, Worsen, or Imitate Symptoms

A range of physical states can produce, worsen, or imitate psychological symptoms. This is not a marginal list of curiosities. Several of these are common. Infection can produce confusion, agitation, and apparent mood change. Particularly in older adults, where an infection elsewhere may present first as mental change. Endocrine disorder is the standard example, and thyroid dysfunction the standard case. An underactive thyroid can produce fatigue, low mood, slowed thinking, and weight change. An overactive one can produce restlessness, irritability, and sleeplessness. Nutritional deficiency can produce fatigue, low mood, irritability. And in severe cases, confusion and memory difficulty. Head injury can change mood, impulse control, attention, and personality. Sometimes with a delay, and sometimes without the person connecting the two. Sustained poor sleep degrades mood, concentration, and emotional regulation. An untreated sleep disorder can closely resemble a mood or attention condition. Many medications prescribed for physical conditions have psychological effects. Some produce symptoms indistinguishable from a psychiatric presentation. And withdrawal from a medication can do exactly the same thing. Finally, both intoxication and withdrawal states can produce mood change and agitation. Diagnosis is unreliable during either, so reassessment after a stable period is standard.

Rule-Out

Why the Order of Questions Matters

Here is the principle. It is simple, and its application is not. Before a presentation is attributed to a psychiatric cause, physical causes are considered. And where indicated, excluded. That is medical rule-out. The reason is asymmetric cost, and the asymmetry is the whole argument. Missing a psychiatric condition delays appropriate treatment, which is serious. Missing a physical condition producing psychiatric symptoms is worse. The actual problem goes untreated, while the person receives treatment aimed at the wrong target. And some of those physical conditions progress while that happens. In practice this is not a single test. It is a sequence of ordinary steps. History first. When did this begin, and what else changed at the same time? What physical conditions are known, and what is the person taking? Including anything recently started, or recently stopped. Then examination and basic investigation, including thyroid function. That is standard before a new diagnosis is settled in most services. Then referral, where the picture includes cognitive change or neurological signs. Or an atypical course. Referral precedes psychiatric treatment rather than following it. Certain features raise the priority of a work-up. Sudden onset in a person with no previous history. Onset at an unusual age. Prominent confusion. Cognitive change out of proportion to mood. Physical symptoms alongside the psychological ones. And any recent change in medication. One thing this is not. It is not skepticism about the person's report. Treatment for distress can begin while investigation proceeds. What waits is the conclusion.

Correlate Or Cause

Four Alternatives That Stay Open

Research regularly reports that a group with a condition differs in some brain measure. Differs from a comparison group, that is. Such a finding is a biological correlate. A physical difference that accompanies a condition. And the step from there to a biological cause is the one most often taken without warrant. The reasoning about correlation applies here without modification. Four alternatives remain open on any such finding. First, the difference may be a consequence of the condition. Living with sustained distress changes sleep, activity, diet, and social contact. Any of those can alter brain measures, making the difference an effect rather than a cause. Second, the difference may be a consequence of treatment. Many participants have received treatment, sometimes for years, and treatments act on the brain. A finding from a treated sample cannot separate the condition from its treatment. Third, the difference may reflect associated behavior. Sleep, exercise, substance use, and social engagement track many conditions. And each has its own effects on brain structure and function. Fourth, a third factor may produce both. Social adversity, poverty, and chronic physical illness are associated with conditions. And they are associated with brain measures independently.

Two Phrases

"Brain Disease" and "Chemical Imbalance"

This is why two phrases need care rather than avoidance. Brain disease, and chemical imbalance. Start with what the evidence does support. Psychological conditions involve the brain. Biological differences are reliably found at group level. And biological interventions change symptoms. All three are well supported. Now what the evidence does not currently support. That any common psychological condition consists in a specific identified brain lesion. Or in a measurable deficiency of a particular chemical. The shorthand misleads in a specific way, and it is worth naming precisely. It implies a demonstrated mechanism where there is an established association. And it implies a physical marker could confirm the diagnosis, which currently it cannot. People do ask whether their condition is chemical, or in the brain. The question usually carries a worry underneath it. Either that the condition is their fault, or that it is permanent. We do not know the cause is accurate, and answers neither worry. It is a chemical imbalance answers the blame worry, and is inaccurate. Research also indicates that purely biological framings can make people more pessimistic. The useful version says the condition is real, and involves the brain and body. That nobody chooses to have it. And that outcome depends on things that can be changed.

Reach And Limits

The Reductionism Objection, at Its Strongest

What does this model explain well? Conditions with a demonstrated physical cause. The effectiveness of physical treatments. The running of conditions in families. The way physical states like sleep loss and hormonal change alter psychological state. And the continuity between human and animal responses in fear and stress. It also produced a genuine ethical gain. Understanding conditions as physical reduced the attribution of blame. What does it leave unexplained? Why this person developed this condition at this time. When someone with similar biology did not. It does not explain the content of psychological experience. Why the worry is about this thing rather than that one. And it does not account for the strong association between social conditions and difficulty. Now the reductionism objection, stated at its strongest. It is not the weak claim that biology is only part of the story. The model's defenders already accept that. It is this. An explanation is only useful if it operates where the causes actually vary. Suppose two people have similar biology and different outcomes. Because one lost a job and the other did not. Then the biological description has recorded the mechanism of transmission. And it has missed the cause. On that view, biological description is not wrong. It is systematically uninformative. This course does not resolve the objection, and you should know it is unresolved.

A Composite Case

A Credible Depressive Picture, Investigated Anyway

One composite case, constructed for instruction, describing no real person. Anita is forty-four, referred with low mood, loss of interest, and poor concentration. She describes feeling slowed down. She sleeps ten hours and wakes unrefreshed, and loses track of conversations. The change began about seven months ago, with no identifiable precipitant. She has no previous psychological history, and describes her circumstances as stable. She has gained weight and feels the cold, and attributes both to inactivity. She has reduced her working hours and stopped attending a weekly class. Ordinary household tasks take twice as long as they did. Three features prompted a medical work-up. Onset was unexplained, in a person with no history. The cognitive slowing was prominent, and out of proportion to her reported mood. And physical symptoms accompanied the psychological ones. Weight gain, cold intolerance, unrefreshing sleep. She had explained each of those away individually. Together they form a pattern. Blood testing showed thyroid function outside the normal range. Once that was treated, her energy, concentration, and mood improved substantially. Her working hours returned to normal, without psychological treatment. Now the reasoning to reproduce, and the last point matters most. This was a fully credible depressive picture. Nothing about it was odd. A clinician who reached that conclusion would not have been careless. Which is exactly why rule-out is routine, rather than reserved for strange cases. And notice what this case does not show. It does not show that depressive presentations are usually thyroid conditions. Generalizing from one composite would be exactly the case-study error.

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FAQ

Questions students ask us

About A Primer on Biological Psychology

What does the biological model of abnormal psychology claim?
The biological model holds that psychological conditions arise from and are expressed through the body, mainly the nervous system but also the endocrine, immune, and metabolic systems. It claims every psychological state has a physical implementation and that changing the physical system can change psychological state. It does not claim that biology is the most important level of explanation or that psychological and social factors are secondary.
Why do doctors check thyroid function before diagnosing depression?
Thyroid problems can closely imitate depression, so physical causes are ruled out before a psychiatric diagnosis is settled. An underactive thyroid can cause fatigue, low mood, slowed thinking, and weight change, while an overactive one can cause restlessness and irritability. Missing a physical cause is costly, because the real problem goes untreated. Sudden onset with no prior history, prominent cognitive slowing, and physical symptoms all raise the priority of a medical work-up.
If brain scans show differences in people with a mental disorder, does that mean the brain difference caused it?
Not necessarily, because a biological correlate is not a biological cause. A brain difference may be a consequence of living with the condition, an effect of past treatment, a result of associated behavior such as poor sleep or substance use, or the product of a third factor like poverty or chronic illness that affects both. Separating these possibilities requires designs that go beyond comparing groups at one point in time.
What is the difference between the sympathetic and parasympathetic nervous systems?
The sympathetic and parasympathetic nervous systems are two branches of the autonomic nervous system with opposite roles. The sympathetic branch mobilizes the body for action by raising heart rate and breathing, sending blood to muscles, and sharpening attention. The parasympathetic branch restores the body afterward by slowing the heart and supporting digestion and recovery. The physical experience of intense anxiety, such as a racing heart and trembling, largely reflects sympathetic activation.

About the Abnormal Psychology course

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Abnormal Psychology (Psychology 180) carries a NCCRS credit recommendation for 3 semester credits. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.
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