Cognitive neuropsychology is a branch of
cognitive psychology that aims to understand how the structure and function of the
brain relates to specific
psychological processes. It places a particular emphasis on studying the
cognitive effects of
brain injury or
neurological illness with a view to inferring models of normal
cognitive functioning. Evidence is based on case studies of individual brain damaged patients who show deficits in brain areas and from patients who exhibit
double dissociations. From these studies researchers infer that different areas of the brain are highly specialised. It can be distinguished from
cognitive neuroscience which is also interested in brain damaged patients but is particularly focused on uncovering the neural mechanisms underlying cognitive processes.
[1]
[edit] History
"
Front and lateral view of the cranium, representing the direction in which the iron traversed its cavity..."
[2]
The modern science of cognitive neuropsychology emerged during the 1960s as a reaction to behaviorism. Scientists realized that there were other sources of data and consciousness became a major area of interest. A particular area of interest for cognitive psychologists was memory. By studying patients with amnesia, which was caused by injuries to the medial temporal cortex, scientists were able to determine the affected areas of the brain. A patient with amnesia will not be able to remember events of the previous day (episodic memory,) but they will still remember how to tie their shoes (procedural memory,) remember a series of numbers for a few seconds (working memory) and be able to recall historical events they have learned in school (semantic memory.)[4][5] Many other studies like this have been done in the field of neuropsychology examining lesions and the effect they have on certain areas of the brain and their functions. [2]
The case of
Phineas Gage was one of the earliest in which a brain injury provided clues to the function of a particular brain area. Gage survived an 1848 accident in which an iron rod 1¼ inches in diameter was driven through one or both of his frontal lobes. Though he suffered no loss of sensory or motor function, Gage's consequent personality changes prevented his return to his position as a railway construction foreman (though most presentations of Gage greatly exaggerate his psychological changes—
see Phineas Gage).
Broca's area and Wernicke's area.
Similarly,
Paul Broca's 1861
post mortem study of an
aphasic patient, known as "Tan" after the only word which he could speak, showed that an area of the left
frontal lobe (now known as
Broca's area) was damaged. As Tan was unable to produce speech but could still understand it, Broca argued that this area might be specialised for speech production and that
language skills might be localised to this
cortical area.
Clues about the role of the
occipital lobes in the
visual system were provided by soldiers returning from
World War I. The small bore ammunition often used in this conflict occasionally caused focal brain injuries. Studies of soldiers with such wounds to the back of their head showed that areas of blindness in the
visual field were dependent on which part of the occipital lobe had been damaged, suggesting that specific areas of the brain were responsible for sensation in specific visual areas, known as
retinotopy.
Most of HM's hippocampus was removed bilaterally.
Studies on
Patient HM are commonly cited as some of the precursors, if not the beginning of modern cognitive neuropsychology. HM had parts of his medial temporal lobes surgically removed to treat intractable
epilepsy in 1953. The treatment proved successful in reducing his dangerous
seizures, but left him with a profound but selective
amnesia. Because HM's impairment was caused by surgery, the damaged parts of his brain were precisely known, information which was usually not knowable in a time before accurate
neuroimaging became widespread. This allowed detailed connections to be made between theories of memory formation and the brain structures removed in HM.
These and similar studies had a number of important implications. The first is that certain
cognitive processes (such as language) could be damaged separately from others, and so might be handled by distinct and independent cognitive and neural processes. (For more on the cognitive neuropsychological approach to language, see
Eleanor Saffran, among others.) The second is that such processes might be localised to specific areas of the brain. Whilst both of these claims are still controversial to some degree, the influence led to a focus on brain injury as a potentially fruitful way of understanding the relationship between
psychology and
neuroscience.
During the 1960s,
information processing became the dominant model in
psychology for understanding mental processes. This provided an important theoretical basis for cognitive neuropsychology, as it allowed an explanation of what areas of the brain might be doing (i.e. processing information in specific and specialised ways) and also allowed brain injury to be understood in abstract terms as impairment in the information processing abilities of larger cognitive systems.
[edit] Methods
By understanding what a person can no longer do, and correlating this with a knowledge of exactly which parts of the
nervous system are damaged, it is possible to infer previously undiscovered functional relationships. This is called the
lesion method.
By using this method, it should also be possible to discover whether a skill is handled by a single cognitive process or a combination of several working together. For example, if a theory states that reading and writing are simply different skills stemming from a single cognitive process, it should not be possible to find a person who, after brain injury, can write but not read or read but not write. This selective breakdown in skills suggests that different parts of the brain are specialised for the different processes and so the cognitive systems are separable.
The
philosopher Jerry Fodor has been particularly influential in cognitive neuropsychology, particularly with the idea that the mind, or at least certain parts of it, may be organised into independent modules. Evidence that cognitive skills may be damaged independently seem to support this theory to some degree, although it is clear that some aspects of mind (such as
belief for example) are unlikely to be modular. Ironically, Fodor (a strict
functionalist) rejects the idea that the neurological properties of the brain have any bearing on its cognitive properties and doubts the whole discipline of cognitive neuropsychology.
Cognitive neuropsychology also uses many of the same techniques and technologies from the wider science of
neuropsychology and fields such as
cognitive neuroscience. These may include
neuroimaging,
electrophysiology and
neuropsychological tests to measure either brain function or psychological performance.
The principles of cognitive neuropsychology have recently been applied to
mental illness, with a view to understanding, for example, what the study of
delusions may tell us about the function of normal belief. This relatively young field is known as
cognitive neuropsychiatry.
[edit] See also
[edit] References
- ^ "The term cognitive neuropsychology often connotes a purely functional approach to patients with cognitive deficits that does not make use of, or encourage interest in, evidence and ideas about brain systems and processes"-- Daniel L. Schater (2000) Understanding Implicit memory: A cognitive neruoscience approach in Michael S. Gazzaniga (ed.) Cognitive neuroscience: a reader. Wiley-Blackwell.
- ^ Harlow (1868)
[edit] Further reading
