Case studies: Phineas Gage, H.M, Paul Broca (1861), Carl Wernicke (1874), Karl Lashley (1929), Sperry (1968)
Localization refers to the concept that specific functions or behaviors are localized (confined) to particular areas or regions of the brain. This principle suggests that different parts of the brain are responsible for distinct psychological processes, such as language, memory, or emotion.
By studying localization, psychologists aim to pinpoint the precise brain regions associated with various cognitive functions, providing valuable insights into human behavior and cognition.
If you’re finding your IB Psychology textbook a bit of a snooze fest and struggling to stay awake, this YouTube video on brain localization is a p good explainer of the brain and its functions.
So how far has psychology gone in trying to prove/ disprove localization?
Are our psychological processes really dictated by specific brain areas?
Here are 4 supportive case studies; 1 contradictory and 1 converging:
Phineas Gage
One notable case study that exemplifies localization is the famous Phineas Gage incident. The railroad construction worker experienced a traumatic brain injury when an iron rod pierced through his skull, damaging parts of his frontal lobe. Following the accident, Gage underwent significant changes in his behavior, demonstrating impulsivity, mood swings, and a lack of inhibition. This case highlights the role of the frontal lobe in regulating personality and social behavior, offering empirical support for the localization of certain cognitive functions within specific brain regions.
| Strengths | Weaknesses |
| – Directly links brain regions to behavior, supports localization | – Limited generalizability due to the uniqueness of the case |
Henry Molaison
H.M underwent a brain surgery in 1953 to treat his severe seizures, which involved the removal of portions of his temporal lobes, including the hippocampus, as a treatment for his epilepsy. While his procedural memory, which involves skills and tasks, remained intact, his inability to create new memories highlighted the critical role of the hippocampus in memory consolidation. This surgical procedure aimed to alleviate the severity and frequency of his seizures.
| Strengths | Weaknesses |
| – Offers insights into memory formation and hippocampal function | – Raises ethical concerns regarding the surgical procedure’s long-term impact on the patient – Unique nature of Patient H.M.’s case may limit the generalizability of findings to broader populations |
Wernicke’s aphasia and Broca’s aphasia are both language disorders that result from damage to specific areas of the brain, typically caused by strokes, traumatic brain injuries, or other neurological conditions. Where Wernicke’s aphasia typically stems from damage to Wernicke’s area, located in the left posterior (hind) hemisphere. Broca’s area refers to the frontal lobe of the dominant hemisphere, usually the left, of the brain with functions linked to speech production.
Paul Broca (1861)
Broca broke ground in highlighting that the left hemisphere is linked to speech articulation. His study of a patient who could only utter “tan” after losing speech at 30 led to the discovery of Broca’s area. Upon death, autopsy revealed a lesion in the left frontal hemisphere, solidifying Broca’s assertion of left hemisphere dominance in speech articulation.
| Strengths | Weaknesses |
| – Demonstrate clear localization of language functions in the brain | – Limited exploration beyond language, relying heavily on lesion studies |
Carl Wernicke (1874)
Wernicke theorized that abnormalities in specific parts of the cerebral cortex can help determine the functions of these regions.
Ie. damage near the auditory cortex in the left brain causes fluent but meaningless speech. His research pioneered understanding of how the brain processes language.
| Strengths | Weaknesses |
| – Demonstrate clear localization of language functions in the brain | – Limited exploration beyond language, relying heavily on lesion studies |
Karl Lashley (1929)
In 1929, Lashley, who aimed to identify memory centers, trained rats to navigate a maze, then removed up to 50% of their cortex. Surprisingly, memory seemed unaffected by specific cortical removals, suggesting a distributed neural network for memory storage. However, questions arise about the applicability of animal research findings to human cognition.
| Strengths | Weaknesses |
| – Challenges simplistic views of memory localization, contributing valuable insights to the understanding of memory processes | – Generalizability: can we apply data in animal studies to humans? – Ethical issues in inflicting harm on subjects |
Sperry (1968)
Sperry (1968) study illuminated the concept of weak localization in brain function. He examined individuals with severed corpus callosum, a conduit that allows signals to transmit from left to right brain hemispheres. When visual stimuli were presented exclusively to the right hemisphere, participants struggled to verbalize responses (left hemisphere is linked to articulation). But when were shown simple words to the same (right) hemisphere, they could successfully identify objects. This suggests language isn’t confined solely to the left hemisphere.
| Strengths | Weaknesses |
| – Research on split-brain patients illuminates brain communication dynamics | – Sample size of 11 is very small and therefore not generalizable to a larger population – All participants were given the same tasks even though they had differences in levels of hemisphere disconnection, hence findings may be affected by individual differeneces |