Difficulty: Introductory | Prerequisites: Basic brain anatomy helpful but not required.
The brain is divided into two hemispheres (left and right), and each hemisphere has specialised functions. Language processing sits mainly in the left hemisphere; spatial awareness in the right. For movement, touch, and vision, each hemisphere controls the opposite side of the body, a principle called contralateralisation. Damage to a specific region can knock out the function it controls, as the classic case of "Tan" demonstrated for speech.
Lateralisation (hemispheric lateralisation)
The principle that certain cognitive functions are predominantly processed by one hemisphere of the brain rather than being equally shared. In simple terms, each side of your brain has its own job specialities.
Contralateralisation
The arrangement whereby each brain hemisphere receives sensory input from, and controls motor output to, the opposite side of the body. Think of it as crossed wiring: your left brain moves your right hand, and vice versa.
Cerebral hemispheres
The two symmetrical halves of the cerebrum, the left hemisphere (LH) and the right hemisphere (RH), connected by the corpus callosum. In everyday language, "left brain" and "right brain."
Frontal lobe
The lobe at the front of each hemisphere, involved in decision-making, planning, voluntary movement, and speech production (via Broca's area on the left side). Think of it as the brain's executive office.
Parietal lobe
The lobe behind the frontal lobe, responsible for processing sensory information such as touch, temperature, and spatial orientation. In simple terms, it helps you feel things and know where your body is in space.
Temporal lobe
The lobe on the side of each hemisphere, near the ears, involved in auditory processing, memory, and language comprehension (via Wernicke's area on the left side). Think of it as the brain's listening and memory centre.
Occipital lobe
The lobe at the back of the brain, primarily dedicated to visual processing. In simple terms, it turns the signals from your eyes into the images you "see."
Broca's area
A region in the left frontal lobe critical for speech production. Damage here causes Broca's aphasia: the patient understands language but struggles to produce fluent speech. This is the area damaged in the case study of "Tan."
Each hemisphere of the cerebral cortex is divided into four lobes, each with distinct responsibilities.
Frontal lobe – sits at the front of the brain. Handles planning, decision-making, voluntary movement, and speech production. Contains Broca's area (left hemisphere), which is essential for producing speech.
Parietal lobe – positioned behind the frontal lobe. Processes touch, pressure, temperature, and spatial awareness. Helps you locate where a sensation is coming from on your body.
Temporal lobe – located on the sides of the brain, roughly behind the ears. Manages hearing, memory formation, and language comprehension (Wernicke's area, left hemisphere).
Occipital lobe – at the very back of the brain. Almost entirely dedicated to processing visual information.
The brain has two hemispheres, left (LH) and right (RH), that look roughly symmetrical but differ in function.
Left hemisphere – dominant for language in most people. This includes speech production, reading, writing, and understanding grammar.
Right hemisphere – dominant for spatial awareness, face recognition, processing emotions, and interpreting non-verbal cues such as tone of voice.
This division of labour is what "lateralisation" refers to: specific cognitive functions lean towards one hemisphere more than the other.
Contralateralisation means each hemisphere processes information from, and sends commands to, the opposite side of the body.
Applies to: movement (motor control), touch (somatosensory processing), and vision (each eye's visual field maps to the opposite hemisphere).
Does not apply to: hearing, smell, or taste. These senses involve input to both hemispheres or have ipsilateral (same-side) pathways.
So damage to the left motor cortex, for example, would impair movement on the right side of the body.
One of the most famous cases in biopsychology. A patient known as "Tan" (his real name was Louis Victor Leborgne) lost the ability to produce speech. The only syllable he could say was "tan," hence the nickname.
Post-mortem examination revealed significant damage to the left frontal lobe, in the region now called Broca's area.
He could still understand language and was cognitively aware, but could not form words.
This case was pivotal evidence for lateralisation: it showed that speech production is localised to a specific area of the left hemisphere.
Students often think people are strictly "left-brained" or "right-brained." They are not. Both hemispheres work together on virtually every task; lateralisation means one hemisphere takes the lead for certain functions, not that the other is idle.
Students sometimes assume contralateralisation applies to all senses. It does not. Hearing, smell, and taste have bilateral or ipsilateral pathways, so they do not follow the crossed-wiring rule.
It is a common mistake to think Broca's area controls all of language. It handles speech production specifically. Language comprehension is primarily the job of Wernicke's area (in the temporal lobe).
Some students confuse lateralisation with localisation. Lateralisation is about which hemisphere dominates for a function. Localisation is about which specific brain region handles a function. Related concepts, different questions.
⚠️ Know which functions lateralise to which hemisphere: language → left, spatial awareness → right. This is one of the most commonly tested points in biopsychology.
⚠️ Be able to explain contralateralisation and name the three modalities it applies to (movement, touch, vision) and the three it does not (hearing, smell, taste).
⚠️ The case of Tan is a staple exam example. Be ready to explain what happened, what it demonstrated about lateralisation, and which brain area was damaged (Broca's area, left frontal lobe).
⚠️ Know all four lobes and at least one key function of each. A labelling question or matching task is likely.
True or false: Language processing is lateralised to the right hemisphere in most people.
Fill in the blank: Contralateralisation applies to movement, touch, and ______.
True or false: Hearing follows the contralateralisation principle.
Fill in the blank: The case study patient "Tan" had damage to ______ area in the left ______ lobe.
True or false: The occipital lobe is primarily responsible for processing sound.
Answers: 1. False (left hemisphere). 2. Vision. 3. False. 4. Broca's; frontal. 5. False (it processes vision; sound is the temporal lobe).
Q: What is hemispheric lateralisation? Give one example.
A: Hemispheric lateralisation is the principle that certain cognitive functions are predominantly processed by one hemisphere of the brain. For example, language is lateralised to the left hemisphere in most people.
Q: Explain contralateralisation. Which senses does it apply to, and which does it not?
A: Contralateralisation means each hemisphere receives input from and controls the opposite side of the body. It applies to movement, touch, and vision. It does not apply to hearing, smell, or taste.
Q: Describe the case of "Tan" and explain what it tells us about brain lateralisation.
A: "Tan" (Louis Victor Leborgne) lost the ability to produce speech following damage to the left frontal lobe, specifically Broca's area. He could still understand language but could only say the syllable "tan." This case provided key evidence that speech production is lateralised to the left hemisphere and localised in Broca's area.
Q: Name the four lobes of the brain and state one function of each.
A: Frontal lobe (planning, voluntary movement, speech production), parietal lobe (touch, spatial orientation), temporal lobe (hearing, memory, language comprehension), occipital lobe (visual processing).
Q: If a patient has damage to the right motor cortex, which side of the body would be affected? Explain why.
A: The left side of the body would be affected, because of contralateralisation: the right hemisphere controls movement on the left side of the body.
This material connects to localisation of brain function more broadly: lateralisation tells you which hemisphere, localisation tells you which specific area. Together they form the foundation for understanding case studies throughout biopsychology.
Contralateralisation links directly to topics on the nervous system and how sensory and motor pathways cross at the brainstem. If you cover the split-brain studies (Sperry and Gazzaniga), those build directly on hemispheric lateralisation.
The case of Tan connects to the wider topic of aphasia (Broca's aphasia vs Wernicke's aphasia) and to debates about how much the brain can recover after damage (neuroplasticity).
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