Parkinsonian emotion recognition impairment better accounted for by sleep deprivation
The New York Times recently covered a paper by Grey and Tickle-Degnen, published in the journal Neuropsychology, finding that people with Parkinson's Disease (PD) are not able to recognize facial and vocal emotions very well. The article states that it's not clear why this seems to be the case.
I briefly reviewed the original meta-analytic paper (the pdf can be found here) and saw that the research team accounted for 1) the emotion recognition tasks used, 2) the medication the participants were on, and 3) the existence of depression as possible moderatoring variables for the impairment in emotion recognition.
They suggest that "the likely cause of this deficit is pathology in neural circuits involved in emotion recognition, particularly within basal ganglia structures including the ventral striatum and STN." This tentative speculation is just fine and dandy, but it doesn't really provide an explanation for why people with PD have this particular deficit in the first place.
They rule out comorbid depression and visualspatial impairment, but go on to postulate that Lewy bodies disease, an abnormal amount of protein found inside the nerve cells of many PD patients, may be affecting their visual cortex, therefore affecting their emotion recognition abilities. Too bad there's no shred of evidence found in the research literature to support this hypothesis (they make sure to note this).
What I found surprising what that they made no mention of sleep disturbances' possible moderating role in explaining their findings. Drawing from my previous entry on sleep deprivation's deleterious effects on emotion recognition, maybe it's the fact that people suffering from PD commonly have concomitant sleep problems, therefore leading to emotion recognition impairment.
Numerous studies have shown that as many as 42% of PD individuals have some kind of sleep disorder (almost four times as many people compared to people without PD). Other studies have found that PD significantly affects rapid eye movement (REM) sleep behavior leading to a variety of cognitive impairments and sleep disturbances (Massicotte-Marquez et al., 2009, Norlinah et al., 2009, Seugnet et al., 2009,). We now also know that REM sleep is crucial in the processing of emotional memory (Nishida, 2008). And like I said before, sleep deprivation takes a heavy toll on emotion recognition functioning (van der Helm, Gujar, & Walker, 2010). Sleep seems to account for much of our emotional life!
In light of the aforementioned studies, it makes the most sense that sleep deprivation from sleep disturbances would be the more likely pathway to emotional recognition impairment in people with PD; not working memory dysfunction as the authors suggest (although it could most definitely exacerbate matters). There may be many potential sources for interpersonal difficulties in PD individuals who are unable to read emotions accurately. Perhaps future sleep treatment can help prevent such difficulties from ever occurring. Just a thought...
Gray HM, & Tickle-Degnen L (2010). A meta-analysis of performance on emotion recognition tasks in Parkinson's disease. Neuropsychology, 24 (2), 176-91 PMID: 20230112
Massicotte-Marquez J, Décary A, Gagnon JF, Vendette M, Mathieu A, Postuma RB, Carrier J, & Montplaisir J (2008). Executive dysfunction and memory impairment in idiopathic REM sleep behavior disorder. Neurology, 70 (15), 1250-7 PMID: 18216303
Seugnet L, Galvin JE, Suzuki Y, Gottschalk L, & Shaw PJ (2009). Persistent short-term memory defects following sleep deprivation in a drosophila model of Parkinson disease. Sleep, 32 (8), 984-92 PMID: 19725249
Norlinah, M., Afidah, K., Noradina, A., Shamsul, A., Hamidon, B., Sahathevan, R., & Raymond, A. (2009). Sleep disturbances in Malaysian patients with Parkinson's disease using polysomnography and PDSS Parkinsonism & Related Disorders, 15 (9), 670-674 DOI: 10.1016/j.parkreldis.2009.02.012