Right hemisphere stroke and the California verbal learning test: a preliminary study.

Method: This study examines group and individual performance on word list recall and recognition in 52 patients with unilateral right hemisphere stroke. Results: On the California Verbal Learning Test, List A, Trials 1-5, patients achieved a mean score of 30.31 (SD = 13.94), which is below the mean standard score of 50 (SD =10) in a normal population. Patients demonstrated below-average performance on other immediate and delayed recall trials and on free- and cued-recall tasks. 67% of patients showed improved performance across learning trials. Conclusion: Results provide support for encoding deficits with reduced rate of learning and inconsistent recall across trials. Key words: memory, right hemisphere damage, stroke, verbal learning

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Memory is a complex process by which an organism registers, stores, retains, and retrieves some previous exposure to an event or experience. It involves a complex network of brain regions including primary and association cortices and the limbic system. Both hemispheres play a role in memory, but they participate differently in terms of the content of information. Individuals with damage to predominantly the right-fronto-temporal polar region may have difficulty retrieving episodic events. (1) Those with damage to the corresponding left hemisphere may have difficulty retrieving semantic information. (2) Furthermore, according to Markowitsch, (3) there may be a hemispheric asymmetry related to storage of information such that the left hemisphere stores primarily verbal or general knowledge (i.e., semantic information) and the right primarily nonverbal or autobiographical (i.e., episodic) information. Consequently, verbal memory is not expected to be impaired in individuals with right hemisphere damage. However, there are a few studies that have addressed verbal memory in this population with conflicting results. (4-7) The purpose of this study is to explore further the impact of right hemisphere damage on verbal learning and memory using the California Verbal Learning Test (CVLT). (8)

The CVLT (8) and the CVLT-2 (9) assess the strategies and processes required for learning and remembering verbal material. They measure the recall and recognition of a list of 16 words over five trials. For the original CVLT, (8) these 16 words represent the four semantic categories of clothes, fruits, spices, and tools. An interference list of 16 words is presented after five learning trials, followed by a free-recall and category-cued recall of the original list. After a 20-minute delay, free recall and category-cued recall of the original list are reassessed. Finally, patients are required to recognize the original 16 words from a list of 44 words.

For this study, the original CVLT was used because data collection began prior to publication of the newer version. The scoring and interpretation of the CVLT provides information about the amount of verbal material learned and how verbal learning occurs or fails to occur. Table 1 lists each measure together with a brief description. Normative data from the CVLT are provided for normal individuals from 17 to 80 years of age, permitting age- and sex-matched performance comparisons. In addition, score patterns for five clinical groups (chronic alcoholism, Parkinson's disease, multiple sclerosis, Huntington's disease, and Alzheimer's disease) are provided.

However, other populations with neurological damage have not been included in the initial normative data of the CVLT. A number of studies have used the CVLT to assess memory and learning problems in these patient groups despite the absence of normative data. For example, deficits in learning across trials, delayed recall, cued recall, and recognition have been identified in patients with traumatic brain injury. (10-14)

Similarly, the CVLT may be a sensitive tool for identifying verbal memory and learning deficits in patients with right hemisphere damage (RHD). For example, Welter using the CVLT found that patients with right hemisphere stroke performed significantly below the norm on all indices, whereas no difference was found between the right hemisphere group and the normative population for the story memory subtests on the Wechsler Memory Scale-Revised. Another preliminary investigation by Cherney and colleagues indicated that a group of 20 patients with RHD demonstrated below average performance on all immediate and delayed recall trials and on both free-recall and cued-recall tasks of the CVLT. (15) These preliminary trends were confirmed with a larger group of 30 patients with RHD by these same investigators. (16) The present study expands the number of participants reported from 30 to 52 and provides more analysis of group …