Clinical Neuropsychology956 Department of Psychological Science

Determination of neurocognitive impairment requires the estimation of preexisting neuropsychological skill level against which to compare obtained post-injury scores.  This estimation historically involved the 50^th percentile of published norms from neurologically intact samples (Pluck, 2023).  As popular U.S. neuropsychological tests were predominantly normed on European American, monolinguals their use with racial/ethnic minorities like African and Hispanic Americans results in elevated rates of false positives (i.e., neurologically intact individuals misdiagnosed with brain injury: Gasquoine & Gonzalez, 2012). 

One proposed solution involves estimating preexisting neuropsychological skill level from performance-based estimates, instead of the 50^th percentile (Gasquoine, 2009; 2022).  Performance-based estimates vary on a case-by-case basis and come from hold measures like vocabulary or irregular word pronunciation test scores that are not affected by the type of brain injury suspected in any given case.  As they are derived from neuropsychological tests they are subject to the same sociocultural influences as the other neuropsychological test scores. 

CN956 is currently investigating the relative accuracy of vocabulary v. irregular word pronunciation hold measures in predicting Wechsler Intelligence Scale Full-Scale IQ in neurologically intact Mexican American balanced bilinguals in both English and Spanish.

References:

Gasquoine, P. G. (2009).  Race-norming of neuropsychological tests. Neuropsychology Review,19, 250-262. http://dx.doi.org/10.1007/s11065-009-9090-5

Gasquoine, P. G. (2022). Performance-based alternatives to race-norms in neuropsychological assessment. Cortex, 148, 231-238.  http://dx.doi.org/10.1016/j.cortex.2021.12.003    

Gasquoine, P. G., & Gonzalez, C. D. (2012). Using monolingual neuropsychological test norms with bilingual Hispanic Americans: Application of an individual comparison standard. Archives of Clinical Neuropsychology, 27, 268–276. https://doi.org/10.1093/arclin/acs004

Pluck, G. (2023). The misguided veneration of averageness in clinical neuroscience. Brain Sciences, 13, 860. https://doi.org/10.3390/brainsci13060860

Among Hispanic Americans (Latinx), 32% are monolingual English-speakers, 5% monolingual Spanish-speakers, with the majority (63%) being bilingual to some degree (Duffin, 2022).  This bilingualism forms a continuum from English-dominant, through balanced, to Spanish-dominant that can be objectively measured by subtracting comparable English and Spanish scores from the Woodcock-Muñoz Language-Survey-Revised (Woodcock et al., 2005: an achievement test) with lower difference scores indicating balance.  In a neuropsychological assessment, language dominant bilinguals should be assessed in their dominant language, but balanced bilinguals can be assessed in either language.  CN956 is investigating the difference in scores between Spanish and English versions of neuropsychological tests among a grouping of neurologically intact, Mexican American, balanced bilinguals.

References:

Duffin, E. (2022). Distribution of English language proficiency among Hispanics in the United States as of 2022. Retrieved from English proficiency among Hispanics U.S. 2021 | Statista 

Woodcock, R. W., Muñoz-Sandoval, A. F., Ruef, M. L., & Alvarado, C. G. (2005). Woodcock-Munoz Language Survey–Revised. Riverside Publishing.

In a single language, neuropsychological test scores differences between bi v. monolinguals have centered within two neurocognitive domains, those of language and executive function.  A consistent finding has been bi < monolingual mean scores on vocabulary and certain other language tests that involve non-frequently used words and time pressure (Celik et al., 2022; Gasquoine, 2016).  This is theoretically explainable from the lower frequency of word use within a given language for bilinguals in comparison to monolinguals.  A less consistent finding (plagued by multiple replication failures) has been of bi > monolingual mean scores on executive function tasks (known as the bilingual advantage: Paap et al. 2020).

Aside from behavioral studies, another way to investigate the presence of the bilingual advantage is to study neural changes within the brain.  Since the Hebbian model was first proposed in the 1940s, learning in the brain has been associated with structural brain changes like long term potentiation (synapse strengthening) and the formation of dendritic spines that lead to novel or enhanced neural pathways.  It is thought that these changes can be documented via static/functional magnetic resonance imaging (MRI/fMRI) measures of: (a) action potentials; (b) grey matter; and (c) white matter.       

The last two decades has seen numerous neuroimaged cross-sectional studies of neurologically intact bi v. monolinguals that are available for CN956 to analyze.

Celik, S., Kokje, E., Meyer, P., Frölich, L., & Teichmann, B. (2022). Does bilingualism influence neuropsychological test performance in older adults? A systematic review.  Applied Neuropsychology: Adult, 29, 855-873. https://doi.org/10.1080/23279095.2020.1788032

Gasquoine, P. G. (2016). Effects of bilingualism on vocabulary, executive functions, age of dementia onset, and regional brain structure. Neuropsychology, 30, 988-997.  https://doi.org/10.1037/neu0000294

Paap, K. R., Mason, L., Zimiga, B., Ayala-Silva, Y., & Frost, M. (2020). The alchemy of confirmation bias transmutes expectations into bilingual advantages: A tale of two new meta-analyses. Quarterly Journal of Experimental Psychology, 73, 1290-1299.https://doi.org/10.1177/1747021819900098

The most important cells of the brain are neurons that are the only cells in the body that do not regenerate after injury.  Consequently, there is no effective treatment for structural brain injury (that involves the loss of neurons) in conditions like Alzheimer disease, the most common form of age-related dementia.  Any life-long behaviors that are proven to reduce the chances of an individual contracting age-related dementia are thus of critical import.  Initial findings that bilingualism delayed the onset of Alzheimer disease in retrospective studies (e.g., Bialystok et al., 2007) have been tempered by replication failures in national, prospective studies (e.g., Lawton et al., 2015) where older neurologically intact individuals were followed over a time period of years to determine who developed dementia. 

Such epidemiological studies have found that individuals who remain physically (and mentally) active as they age are less likely to develop age-related dementias (Hamer & Chida, 2009).  Based on animal models it was hypothesized that physical exercise was promoting neurogenesis (regeneration of neurons) or synaptogenesis.  This has been tested in numerous randomized controlled clinical trials of older participants with post minus pre neuropsychological test scores as the outcome measures.  Review and meta-analysis of these studies found no evidence of physical activity related neuropsychological test score gains in the domains of delayed memory (Gasquoine, 2018) or executive function (Gasquoine & Chen, 2022), the first two neurocognitive domains negatively affected in age-related dementias.  One limitation of this research is that all participants were sedentary prior to the study.  Nevertheless, this research suggests that the effect of physical exercise on reducing the chances of contracting age-related dementia may be due to an enhanced immune system.  What triggers the onset of age-related dementias remains unknown, an opportunity for CN956 continued attention.

References:

Bialystok, E., Craik, F. I. M., & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45, 459–464. https://doi.org/10.1016/j.neuropsychologia.2006.10.009

Gasquoine, P. G. (2018). Effects of physical activity on delayed memory measures in randomized controlled trials with nonclinical older, mild cognitive impairment, and dementia participants, Journal of Clinical and Experimental Neuropsychology, 40, 874-886. https://doi.org/10.1080/13803395.2018.1442815

Gasquoine, P. G., & Chen, P.-Y. (2022) Effect of physical exercise on popular measures of executive function in older, nonclinical, participants of randomized controlled trials: A meta-analytic review. Applied Neuropsychology: Adult, 29, 203-211. https://doi.org/10.1080/23279095.2020.173298

Hamer, M., & Chida, Y. (2009). Physical activity and risk of neurodegenerative disease: A systematic review of prospective evidence. Psychological Medicine, 39, 3–11.https://doi.org/10.1017/S0033291708003681

Lawton, D. M., Gasquoine, P. G., & Weimer, A. A. (2015). Age of dementia diagnosis in community dwelling bilingual and monolingual Hispanic Americans. Cortex, 66, 141–145. http://dx.doi.org/10.1016/j.cortex.2014.11.017

All neuropsychological tests require effort on the part of the patient to obtain valid scores.  In certain situations, such as forensic assessments, it may benefit a patient to appear more neurocognitively impaired than they actually are.  Clinical neuropsychologists can administer performance validity measures in the course of an assessment to check if this is occurring.  Performance validity measures have research determined cut-scores that separate valid from invalid performance.  These cut scores were derived from samples of European American monolinguals and so may not be suitable for Hispanic American (Latinx) bilinguals.  CN956 is investigating the efficacy of performance validity measures with bilingual Hispanic American and have discovered to date that all studied (Test of Memory Malingering; Dot Counting; California Verbal Learning Test Forced Choice; Rey 15-IR; except Reliable Digit Span are acceptable (Gasquoine et al., 2017; 2019).

Gasquoine, P. G., Weimer, A. A., & Amador, A. (2017). Specificity rates for non-clinical, bilingual, Mexican Americans on three popular performance validity measures. The Clinical Neuropsychologist, 31, 587-597. https://doi.org/10.1080/13854046.2016.1277786

Gasquoine, P. G., Weimer, A. A., & Orta, M. (2019). Specificity rates for non-clinical, bilingual, Mexican Americans with California Verbal Learning Test3, Verbal Fluency, and Rey 15-IR performance validity measures. The Clinical Neuropsychologist, 33, 1445-1454. https://doi.org/10.1080/13854046.2018.1530374