Biopsychology

This is Unit Two of Psychology, Part Two: the brain, the glands, and the genes. Part One built the hardware from a single cell up to the wiring diagram. This part starts where that stopped and works upward through the brain, then outward into two systems that influence behavior without being nervous tissue at all. The best sequence in this part is a method followed by five patients. The method is how a deficit gets localised — name the region whose damage produces it, then check that against what the patient has retained. Then five cases, each one a person who can do something and cannot do something adjacent to it. There is a myth in here too, and it is the most widespread false claim about the brain in general circulation. Hemispheres do specialise. People are not left- brained or right-brained, and the entry says exactly where the real finding stops and the invention starts. Then genetics, and one statistic that gets misapplied constantly — because it is a property of a population and gets read as a property of a person. By the end you will be able to do five things. One: say what each of the four subcortical structures does. Two: localise a deficit to a lobe. Three: say what lateralisation means and what the popular claim adds. Four: say what heritability is a proportion of. Five: say what range of reaction cannot do.

Three entries dividing the brain into regions, and the order is meaningful. The first handles the things that have to keep happening whether or not anybody is paying attention, and each region after it handles something less immediately essential and more distinctly human.

The first region.

Psych 0199 The Hindbrain

The medulla, pons and cerebellum — managing basic life support and coordinated movement. The functions that cannot be interrupted, in the region furthest from thought.

The second.

Psych 0201 The Midbrain

Structures involved in movement, arousal, and the orienting of attention toward sudden stimuli. Turning toward a noise happens here, before any decision about it.

The third.

Psych 0203 The Forebrain

The cerebral cortex and the structures beneath it, handling complex thought and emotion. The largest region, and the one the rest of this topic works through.

Four entries, and each does one job that the whole system depends on. One of them is required for forming new memories — not helpful for, required — and that word is why a person can lose the ability to form them while keeping everything they already had.

The relay.

Psych 0205 The Thalamus

Relaying incoming sensory signals to the appropriate regions of the cortex — with smell as the single exception, which reaches the cortex without passing through.

The regulator.

Psych 0207 The Hypothalamus

Regulating hunger, thirst, body temperature and sexual behavior, and controlling the pituitary gland. It is the link between the nervous system and the glands in Topic Seven.

Memory's requirement.

Psych 0209 The Hippocampus

Required for forming new long-term memories of facts and events. Required, so damage takes away the forming of new memories and leaves the old ones in place.

Significance.

Psych 0211 The Amygdala

Processing emotional significance, and central to fear learning and threat detection. It decides that something matters, before anything decides what to do about it.

Five entries. The outer layer and its four regions — and it is worth holding these precisely rather than approximately, because the next two topics are entirely about telling them apart from the outside.

The layer.

Psych 0213 The Cerebral Cortex

The folded outer layer of the forebrain, where perception, language and reasoning are carried out. Folded, because surface area is the constraint.

The front.

Psych 0215 The Frontal Lobe

Planning, judgment, voluntary movement, and the inhibition of impulses. Inhibition is on the list — stopping is a function, not the absence of one.

The top and back.

Psych 0217 The Parietal Lobe

Touch, temperature, pain, and the position of the body in space. Knowing where your own limbs are is a computation, performed here.

The rear.

Psych 0219 The Occipital Lobe

Processing visual information arriving from the eyes. At the back of the head, as far from the eyes as the cortex allows.

The sides.

Psych 0221 The Temporal Lobe

Hearing, language comprehension, and the recognition of faces and objects. Recognition is separate from seeing, which the case entries make concrete.

Two entries, and they sit in different lobes doing halves of one thing. Producing speech and understanding it are separable — which sounds abstract until the case entry shows what it looks like when one half is gone.

Production.

Psych 0223 Broca's Area

In the frontal lobe, required for producing fluent speech. Damage leaves comprehension in place and takes the fluency.

Comprehension.

Psych 0224 Wernicke's Area

In the temporal lobe, required for comprehending language. Damage leaves fluent, well-formed speech in place and takes the meaning out of it — which is the strangest deficit in the unit.

Six entries, and this is the best-constructed sequence in the unit. A method first, then five patients — and every one of the five is defined by a pair: something they can still do perfectly, and something adjacent they cannot do at all.

The method.

Psych 0226 Locating a Function by Lobe

Naming the lobe whose damage produces the deficit, then checking that against what the patient has retained. The second half is the check — a wrong localisation predicts the wrong retained abilities.

The first patient.

Psych 0227 Case: The Patient Who Cannot Name Faces

A patient who sees a face clearly and cannot say whose it is has temporal lobe damage. Vision intact, recognition gone — which localises it away from the occipital lobe.

The second.

Psych 0229 Case: The Patient Who Speaks Fluent Nonsense

A patient producing fluent, well-formed sentences carrying no meaning has damage to Wernicke's area, in the temporal lobe. The speech machinery is working; what it is being handed is not.

The third.

Psych 0231 Case: The Patient Who Cannot Plan a Meal

A patient who can name every step of a task and cannot sequence or begin them has frontal lobe damage. The knowledge is intact and the organising of it is not.

The fourth.

Psych 0233 Case: The Patient Blind with Healthy Eyes

A patient whose eyes and optic nerves are undamaged and who cannot see has occipital lobe damage. The eyes are a camera, and the seeing happens elsewhere.

And the fifth.

Psych 0235 Case: The Patient Who Cannot Locate Touch

A patient who feels a touch and cannot say where on the body it landed has parietal lobe damage. Sensation and location are separate computations, and only one of them failed.

Four entries. A real asymmetry, the popular claim that inflates it into a personality type, what happens when the two halves are surgically disconnected, and then the capacity that limits how permanent any of this is.

The real finding.

Psych 0237 Lateralization

Some functions being handled more by one hemisphere than the other. More by — a tendency in a distribution, not an assignment.

And the myth.

Psych 0238 The Left-Brain / Right-Brain Myth

Individuals are not left-brained or right-brained, with one hemisphere driving their personality or aptitude. The real finding is about which side handles a function; the myth is about which side runs a person.

Cutting the connection.

Psych 0240 The Corpus Callosum and Split-Brain Findings

The corpus callosum connects the hemispheres, and severing it leaves each without the other's information. The findings from those patients are where lateralisation was actually established.

And reorganisation.

Psych 0242 Neuroplasticity

The nervous system's capacity to reorganise its structure and connections in response to experience or injury. It makes every localisation in this unit a description of the usual case rather than a fixed law.

Four entries on a second signalling system. It uses the bloodstream instead of nerves, which makes it slower and much more widely distributed — and one gland in it takes its orders from the brain structure named earlier.

The system.

Psych 0244 The Endocrine System

A network of glands releasing hormones into the bloodstream to regulate bodily processes. Slower than nerve signalling, and reaching everywhere the blood reaches.

The director.

Psych 0246 The Pituitary Gland

Releasing hormones that direct other endocrine glands, under the control of the hypothalamus. A chain of command running from brain to gland to gland.

Under stress.

Psych 0248 The Adrenal Glands

Releasing epinephrine and cortisol, mobilising the body's response to stress. The same mobilisation the sympathetic division produced in Part One, by a slower route.

The rate-setter.

Psych 0250 The Thyroid Gland

Releasing hormones regulating metabolic rate, growth and energy level. It sets a baseline everything else operates against.

Five entries, and one of them corrects a statistic that is misread more often than it is read correctly. Heritability is a number about variation in a population. It is not a number about how fixed anything is in any individual person.

The units.

Psych 0252 Genes and Chromosomes

A gene is a segment of DNA coding for a protein; chromosomes are the structures carrying genes. Protein is the actual output — everything else is downstream of that.

Two words.

Psych 0254 Genotype and Phenotype

The genotype is the genetic inheritance; the phenotype is the observable characteristics actually developed. One is what was received, the other what happened.

The statistic.

Psych 0256 Heritability

The proportion of variation in a trait, within a specific population, attributable to genetic differences. Variation, and within a specific population — both qualifications are part of the number.

And the misreading.

Psych 0257 Misreading Heritability

It is an error to read heritability as the degree to which a trait is fixed in an individual. The number describes differences across a group, and says nothing about any one member of it.

Expression.

Psych 0259 Epigenetics

Changes in gene expression caused by environmental factors, without changes to the DNA sequence. The sequence is fixed and what gets read from it is not.

Three entries closing the unit. An idea about the shape of the gene-environment relationship, then an unusually honest entry saying what that idea cannot be used for — and then the capstone, which traces one behavior from gene to environment without skipping a level.

The idea.

Psych 0261 Range of Reaction

Genetics setting upper and lower bounds on a trait while environment determines where within them a person falls. A shape for the relationship rather than a percentage split.

And its limit.

Psych 0262 What Range of Reaction Cannot Do

It cannot be measured for any individual, because a person's genetic bounds are never directly observed. A useful idea about how the relationship works that yields no number for anybody.

The capstone. One behavior, traced.

Psych 0264 From Gene to Behavior, Traced

Tracing a behavior biologically means moving from gene to protein to circuit to hormone to environment and back, without skipping a level. Every level in this unit, in one chain.

Five things you can now do, and Unit Two is complete. You can say what the four subcortical structures do — a relay for everything but smell, a regulator of hunger and temperature, the requirement for forming new memories, and the detector that decides something matters. You can localise a deficit to a lobe by naming the region and checking it against what the patient retained — recognition without vision, fluency without meaning, knowledge without sequencing. You can say what lateralisation means and where the myth departs from it: some functions are handled more by one hemisphere, and no person is run by one. You can say what heritability is a proportion of — variation within a specific population — and that it describes nothing about any individual. And you can say what range of reaction cannot do: it cannot be measured for any individual, because nobody's genetic bounds are ever observed directly.