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The art and science of neuropsychology

Neuropsychology is a branch of psychology that is concerned with how the brain and the rest of the nervous system influence a person’s cognition and behaviors. More importantly, professionals in this branch of psychology often focus on how injuries or illnesses of the brain affect cognitive functions and behaviors.

This articles is aimed as a refresher for those familiarizing themselves with the common tests and parameters evaluated in neuropsychology assessment of common functional brain disorders.


Prose Passage Recall


Prose Passage Recall is a subset of the Wechsler Memory Scale also known as the logical memory test. It is primarily a test of verbal learning (verbal memory) involving acquisition and registration of memory for spoken materials. Long-term memory is divided into declarative and non-declarative types. Declarative memory itself is also divided into two categories of episodic and semantic memory. Episodic memory involves memory of specific time and personal events, where the individual can remember her episodes occurring. Verbal memory is categorised as episodic memory. Prose passage test involves immediate free recall after auditory presentation and subsequent delayed recall of the previously presented auditory information, thus assessing the ability of individual’s verbal memory. Tests that measure the delayed recall of prose passages are very sensitive to verbal memory deficits.

The medial temporal cortex including the hippocampus is closely associated with episodic memory function. This is consistent with data from functional neuroimaging studies in humans that confirm the involvement of medial temporal lobe structures such as the hippocampus and the associated parahippocampal areas in memory performance. In particular, memory for verbal information has been commonly linked to the left medial temporal lobe of the left hemisphere of the brain. Therefore damage to medial temporal cortices is expected to manifest in episodic memory impairment. Therefore, prose passage recall is a good assessment of left hemisphere function especially that of the left medial temporal cortex.


Digit Span Test


The digit span test (both forward and backward variant) is often used as a tool for measuring an individual’s immediate auditory memory and verbal working memory as well as its number storage capacity. Working memory is the part of the cognitive system that acts as a temporary medium for storage and manipulation of information. The abilities of verbal working memory are dependent on its specialised components, especially the ‘phonological loop’, which consists of a verbal storage system and a rehearsal system. During the digit span test, subjects often mentally repeat the digits presented to them, thus rehearsing them, this facilitates the entry of the visual inputs into the short-term verbal store.

Data from functional neuroimaging in humans and lesion experiments in animals shows that working memory performance is correlated with local brain morphology in the frontal cortex, parietal cortex and anterior cingulate cortex, with partial involvement of the basal ganglia. Thus individuals with frontal lobe lesions may display impairments in the digit span test.


Wisconsin card sorting test


The Wisconsin Card Sorting Test (WCST) is widely used as a measure of the brain’s executive functions, specifically the ability to show mental flexibility in the face of changing schedules of reinforcement and control of perseverative responses. WCST allows us to assess functions that are associated with the frontal lobe, such functions include strategic planning, organised searching and using environmental cues to alter cognitive sets and change behaviour for achieving a specific goal, all whilst controlling impulsive responses. Failure in this test could signify ‘executive dysfunction’ which could arise from deficits in cognitive functions such as as attention, working memory and processing of visual material

The Wisconsin Card Sorting Test is often referred to as a test of “frontal lobe” function. This is mainly due to observations wherein patients with frontal lobe lesion generally perform inadequately at the test. In particular, patients with dorsolateral frontal lobe lesions make a higher rate of perseverative errors compared to the control participants. Early Positron Emission Tomography (PET) studies show that tasks involved in this test, lead to significant activation of the dorsolateral prefrontal cortex.


Verbal Fluency Test


The Verbal fluency Test is often used as an efficient screening instrument of executive functions, in particular general verbal functioning. It allows us to see how people perform in tasks that encourage deep semantic encoding and allows for assessing semantic or serial clustering during tests of short and long delay recall, thus enabling us to distinguish between encoding, storage and retrieval of information deficits. Different word clustering patterns exist between patients and healthy individuals. People tend to change from one cluster of words to another a different number of times in any given theme. This assesses strategy formation and tests behavioural flexibility to switch from one cluster to another.

Neuropsychological investigations regarding the areas of the brain involved in the verbal fluency test show that both frontal and temporal lobes are involved, with the former being more involved in the phonemic variant and the latter in the semantic (meaning based) variant of the test. Thus patients with neurological pathologies in these areas often display impairments in either or both versions of the test. Verbal fluency scores depend on the integrity of the individual’s broca’s area (posterior inferior frontal gyrus) and also the dorsolateral prefrontal cortex. Number of switches between clusters depends more on the dorsolateral prefrontal cortex. More commonly, individuals with left dominant frontal lobe lesions show impairments in verbal fluency.

 

  • Fronto-temporal dementia.

Since fronto-temporal dementia involves impairment of the frontal and temporal lobes, individuals suspected of having this condition should undergo neuropsychological assessment that test the brain’s executive functions and memory capacity, as these lobes are primarily involved in said functions respectively.

Classic tests of executive function such as Wisconsin Card Sorting Test, Verbal Fluency test, Stroop test, and Digit Span and Trail Making test are reasonably appropriate exams for assessing patient’s frontal lobe function. In addition, the Weschsler memory scale subsets can be used to measure the extent of temporal lobe lesion and their behavioural manifestations. Such tests include prose passage recall test and word list learning, which are both used for measuring declarative memory function. Furthermore, the Rey Osterrieth complex figure test can also be used for assisting in measurement of executive function that is mediated by the prefrontal lobe. This test can also shed light on the hemisphere dominance of the individual and whether their brain lesion is unilateral or bilateral.

Tests of verbal fluency, stroop test, and performance on Wisconsin Card Sorting Test should be poorer in-patient with fronto-temporal dementia. These results will be consistent with the known clinical deficits that we see including difficulty in planning, problem solving, increased impulsive behaviour, difficulty in inhibiting inappropriate responses in addition to problems in understanding social feedback cues.

We can also expect some mild memory impairment, manifesting as a secondary effect of executive dysfunction, (poor attention, concentration and planning) and not because of extensive temporal lobe damage. Therefore, it is unlikely to see any significant memory impairment in patients with fronto-temporal dementia.

  • Alzheimer’s disease

This Condition is characteristically linked to memory deficits. This is expected as Alzheimer’s disease primarily affects the hippocampus and temporal lobe where memory processing occurs, involving both the short-term memory (working memory) and declarative portion of long-term memory respectively. This disorder of memory processing linked to temporal lobe dysfunction usually leads to struggle in acquiring new memories and difficulty in recalling recently observed facts, which is consistent with observations such as  difficulty in remembering prearranged meeting and appointments with friend and family. Her facing problems in remembering peoples name is also a manifestation of Alzheimer’s disease and temporal lobe dysfunction, affecting her declarative memory, where the patient finds it challenging to recall facts gathered during specific experiences such as remembering names of people who he/she has been previously acquainted with.

For example, if a patient shows impairment for both verbal and visual material and spatial information (e.g. not realising she has a messy house) suggests bilateral involvement of the temporal lobes resulting in impairment in every declarative memory sphere (both episodic and semantic) irrespective of modality, all of which can be the characteristics of Alzheimer’s disease.

In Alzheimer’s disease, episodic memory loss is the earliest and most prominent feature of dementia of AD followed by loss of semantic memory. Here, we can expect impairments in tests such as word list learning whereby Mrs K will show a tendency towards a primacy deficit, that is she tends to forget items presented earlier in the word list. Therefore, she’s expected to show general impairment in delayed recall tests.

Patient’s may also exhibit deficits in verbal and visuospatial abilities. The Rey Osterrieth complex figure test can best evaluate their nonverbal memory function, particularly of the right temporal lobe. In addition, Kendrick’s object learning and spatial object location tests (recall of objects after brief exposure) are useful for evaluating the nonverbal memory function and helps in distinguishing between dementia and depression in elderly. In this case a poor recall is expected on both tests.

Such a patient is also expected to show signs of anterograde amnesia, since temporal lobe damage is documented to lead to anterograde memory deficit, which is the loss of ability to form new memories after the onset of the underlying brain pathology, leading to a partial or complete impairment in recalling the recent past, while long term memories before then remain relatively unscathed.

  • Parkinson’s disease

There is a substantial cognitive heterogeneity amongst patients affected with Parkinson’s disease, which is evident in various profiles and levels of severity. Therefore cognitive impairments affect most people with Parkinson’s disease. The same brain changes that result in the motor symptoms can also affect memory and thinking, often slowing them down. Since Parkinson’s disease is associated with basal ganglia pathology, it is usually accompanied by classic basal ganglia disorders including frequent experience of cognitive dysfunction, including memory deficits, depression and most notably deficits in executive functions.

In addition, the severity of cognitive symptoms in Parkinson’s disease can partially be a knock on effect from the severity of the motor symptoms. One of the earliest and most affected domains of cognitive skills in PD patients is executive function. Hence, poor performance in tasks of executive function such Wisconsin Card Sorting Test is expected.

In terms of attentional skills, simple tests such as repeating a series of digits or short word list learning should be relatively unimpaired. Language skills are expected to be unimpaired in PD aswell, with their vocabulary remaining intact. However, tests of verbal fluency (both semantic and phonemic fluency) in PD patients might show some deficits, but these are most likely a secondary effect of executive dysfunction rather than lexical impairment. Visuospatial skills are difficult to measure in patients with motor deficits, but certain aspects such as visual discrimination and pattern completion are expected to be impaired.

 


References:

  1.  Posner, M. I.; Digirolamo, G. J. (2000). “Cognitive neuroscience: Origins and promise”. Psychological Bulletin126 (6): 873–889. doi:10.1037/0033-2909.126.6.873PMID 11107880.
  2. “The Great Canadian Psychology Website – Researchers”. University of Calgary. Retrieved 14 August 2017.
  3. Finger, Stanley (2000). Minds Behind the Brain: A History of the Pioneers and their discoveries. New York: Oxford. pp. 22ISBN 978-0-19-518182-1.
  4. Highfield, Roger. “How Imhotep gave us medicine”The Daily Telegraph. Retrieved 24 March 2018.
  5. Carus, Paul (1905). “The Conception of the Soul and the Belief in Resurrection Among the Egyptians”. The Monist15 (3): 409–428. doi:10.5840/monist190515326JSTOR 27899609.

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