What the exam asks
- Split-brain scenarios: Predicting whether a patient with a severed corpus callosum can verbally name or physically point to an object flashed to their left or right visual field.
- Aphasia differentiation: Distinguishing between damage to Broca’s area and Wernicke’s area from descriptions of a patient’s speech.
- Neuroplasticity: Explaining how younger brains or brains practicing new skills physically reorganize so undamaged regions take over lost functions.
- Research methods evaluation: Choosing between EEG, fMRI, case studies, and lesioning based on what a researcher needs to measure, and identifying the methodological limits (such as generalizability or causation) of each.
Core ideas
Hemispheric specialization and split-brain research
The cerebral cortex is divided into two hemispheres connected by the corpus callosum, a wide band of axon fibers. Each hemisphere exhibits contralateral organization: the left hemisphere receives sensory input from the right visual field and controls the right side of the body, while the right hemisphere receives input from the left visual field and controls the left side of the body.
In most people, the left hemisphere specializes in language, speech, and logical analysis, whereas the right hemisphere specializes in spatial reasoning, facial recognition, and perceptual tasks.
To treat severe epilepsy, surgeons sometimes sever the corpus callosum, creating a split-brain patient. Research by Roger Sperry and Michael Gazzaniga used this procedure to test each hemisphere separately:
| Visual field where image is flashed | Hemisphere that receives it | Can the patient say the word out loud? | Which hand can select the hidden object by touch? |
|---|---|---|---|
| Right visual field (RVF) | Left hemisphere (has language areas) | Yes | Right hand (controlled by left hemisphere) |
| Left visual field (LVF) | Right hemisphere (lacks speech production) | No (cannot share info with left hemisphere) | Left hand (controlled by right hemisphere) |
Language areas and aphasia
In the vast majority of individuals, language processing is lateralized to the left hemisphere. Damage to specific cortical areas causes aphasia (impaired language ability):
- Broca’s area (left frontal lobe) controls speech production via the motor cortex. Damage causes Broca’s aphasia (expressive aphasia): patients comprehend speech well and know what they want to say, but struggle to form words, speaking in slow, labored, telegraphic phrases.
- Wernicke’s area (left temporal lobe) controls language comprehension. Damage causes Wernicke’s aphasia (receptive aphasia): patients speak fluently with normal rhythm, but produce meaningless “word salad” and cannot understand spoken or written language.