Localization - IB Psych

Wilder Penfield - Mapping Sensory & Motor Cortex

- Attempts to establish strict localization of function have culminated in the creation of cortical maps. - Used neural stimulation to, stimulation parts of the cortex with electrodes and observed the effects it had on sensations and behavior. - He uncovered the entire cortex, and his map is a relative representation of various parts of the body in the cortex.

Karl Lashley (1929)

Contrary research to strict localization states that psychological functions may be localized anywhere in the brain: Karl Lashley (1929) claimed that memory of a maze in rats was distributed rather than localized.

Corkin (1997)

Aim: To investigate the extent of the hippocampal and medial temporal lobe damage to H.M.'s brain and to determine whether this could be sufficient to have resulted in drastic memory loss suffered by H.M. Method: case study; observational Participants: H.M., a man who suffered from amnesia after hippocampal surgery. Procedure: One MRI scan was conducted on H.M. in 1992 and one in 1993. Prior to the first MRI, H.M. completed an IQ test and a memory test. The IQ test showed that he had normal intelligence, but the memory test showed his memory quotient (MQ) was 37 points lower than his IQ and showed he had severe amnesia. Results: Both scans showed that the lesioning (also called ablation or cutting) of H.M.'s Brain was 3m less than Scoville had estimated. It therefor did not extend as far into the posterior hippocampal as he thought, although there was surrounding damage, as stated, to the uncus and the amygdala. Approximately 50% of the posterior hippocampus on each side reminded, but this had shrunk considerably on the right side. Corkin. Et. al. believed that this could be due to both the removal of the rest of the hippocampus and due to the drugs/continuing, though reduced, epileptic seizures. Conclusions: The small amount of normal hippocampus remaining in the left temporal lobe was not sufficient to support normal memory. Therefor, this study demonstrates the importance of the hippocampus and the temporal medial lobe area for memory. Evaluation Strengths: similar findings of weak localization in regards to memory in Milner et al (1968)/Lashley (1929); ethical, the researchers merely observed the effects of H.M.'s extenuating circumstances Limitations: Population validity is low, as only a single person participated in the study; gender bias, male only; cultural bias, the study wasn't replicated cross culturally, conducted in America; cognitive/sociocultural factors are ignored; questionable ethics - was he able to consent every time? Not replicable Application: further insight into weak localization, with two parts of the brain being shown to be responsible for memory.

Sperry (1968) & Gazzaniga (1967)

Aim: to investigate how the two hemispheres function independently when the connection between them is severed. Participants: four patients who underwent novel treatment for epilepsy that involved surgically cutting the corpus callosum. Method: in-depth case study of four unique individuals. Procedure: A technique was used that allowed researchers to project stimuli to either the left or the right eye of the participant. They used a table with a long board on it. Participant sat in front of the board, fixing their eyes on the dot in the center. Stimuli were then flashed on the far right of the far left of the board for 1/10 of a second. For some trials, the table also had a curtain with some objects behind it. Participants could reach behind the curtain and feel the objects with their hands. Results: When a picture of a spoon was shown to the left visual field (connected to the right hemisphere) and participants were asked to describe the object, they said nothing. However, when asked to pick an object behind the curtain, they could feel around and pick a spoon but only with their left hand (because it is connected to the right hemisphere). Participants could not explain why they pick the spoon. This result supports the idea that language is localized in the left hemisphere— When a simple word (such as "pencil") was flashed to the right hemisphere, participants were able to reach behind the curtain and pick a pencil, contrary to the previous finding, showing that the right hemisphere's able to process some simple speech. Weak localization of language comprehension is shown. When researchers placed for plastic letters in a pile behind the curtain and asked participants to "spell a word," one participant was able to spell "love" with his left hand. He was not able to name the word he just spelled. This shows that even language production may be present in the right hemisphere and some, but not all, people. Conclusion: these results support the idea that localization of language is not strict. First, language production is in language comprehension, mostly focused on the left hemisphere, but the right atmosphere can also perform some simple tasks. Evaluation Strengths: ethical, they simply observed people with epilepsy; similar findings - Corkin (1997) and Lashley (1929) also found that localization to not be strict Limitations: small sample size; low population validity;cultural bias; potential gender bias, as participant's genders aren't specified; ignored cognitive/sociocultural factors. Application: further insight into weak localization, showing that language is affected in multiple areas of the brain

Wernicke

Carl Wernicke (1874) discovered the brain area responsible for comprehension of written and spoken language. Wernicke's area is located in the temporal lobe of the dominant hemisphere, usually on the left. People with Wernicke's aphasia have an impairment of speech comprehension, but their articulate speech is intact.

Broca

Paul Broca (1861) documented the case study of "Tan", a patient who'd lost the ability to speak or write but had retained all other functions such as intelligence and speech comprehension. He understood everything said to him, but the only sound he could make was the syllable "tan". The loss of articulated speech became known as Broca's aphasia. An autopsy later revealed a specific lesion in Tan's left hemisphere, in the posterior inferior frontal gyrus. This is now known as Broca's area.

Practice Exam Questions

SAQ: Describe one study related to localization of function. ERQ: Evaluate research on localization of function with regard to memory.

Widely distributed functions

functions that can't be localized anywhere in the brain

Relative Localization of Function Summary

some functions are indeed strictly localized. Examples include Broca's aphasia and Wernicke's aphasia. Some functions such as memory are widely distributed. Some functions are weakly localized — several brains are responsible for the same function, but one of these areas is dominant. This is illustrated by split brain research. Some components of a function may be localized while other components of the same function may be distributed. For example, speech production seems to be more localized in speech comprehension. Localization is not static: brain areas can re-specialize due to neuroplasticity

Weak localization

the idea that one brain area may be responsible for a function, but not exclusively, and other areas may take over the function.

Strict localization

the idea that there is a clear correspondence between psychological functions and brain areas, and that all functions can be mapped onto the brain.

Localizations of function

the theory that certain areas of the brain are responsible for certain psychological functions.