What Is Mental Effort: A Clinical Perspective.

Although mental effort is a frequently used term, it is poorly defined and understood. Consequently, its usage is frequently loose and potentially misleading. In neuroscience research, the term is used to mean both the cognitive work that is done to meet task demands and the subjective experience of performing that work. We argue that conflating these two meanings hampers progress in understanding cognitive impairments in neuropsychiatric conditions because cognitive work and the subjective experience of it have distinct underlying mechanisms. We suggest that the most coherent and clinically useful perspective on mental effort is that it is a subjective experience. This makes a clear distinction between cognitive impairments that arise from changes in the cognitive apparatus, as in dementia and brain injury, and those that arise from subjective difficulties in carrying out the cognitive work, as in attention-deficit/hyperactivity disorder, depression, and other motivational disorders. We review recent advances in neuroscience research that suggests that the experience of effort has emerged to control task switches so as to minimize costs relative to benefits. We consider how these advances can contribute to our understanding of the experience of increased effort perception in clinical populations. This more specific framing of mental effort will offer a deeper understanding of the mechanisms of cognitive impairments in differing clinical groups and will ultimately facilitate better therapeutic interventions.

Psychotic illness in people with Prader-Willi syndrome: a systematic review of clinical presentation, course and phenomenology.

BACKGROUND: Prader-Willi syndrome (PWS) is a rare and complex neurodevelopmental disorder resulting from absent paternal expression of maternally imprinted genes at chromosomal locus 15q11-13. This absence of expression occurs as a consequence of a deletion on the chromosome 15 of paternal origin (ca. 70%), a chromosome 15 maternal uniparental disomy (mUPD; ca. 25%), or an imprinting centre defect (IC; ca. 1-3%). At birth, individuals with PWS are severely hypotonic and fail to thrive. Hyperphagia and characteristic physical and neuropsychiatric phenotypes become apparent during childhood. The risk for the development of a co-morbid psychotic illness increases during the teenage years, specifically in those with PWS due to the presence of an mUPD. The primary aim of this literature review is to inform clinical practice. To achieve this, we have undertaken a systematic analysis of the clinical research literature on prevalence, presentation, course, characteristics, diagnosis and treatment of psychotic illness in people with PWS. The secondary aim is to identify clinical aspects of psychotic illness in PWS in need of further investigation. METHODS AND FINDINGS: A systematic literature review on psychosis in PWS was conducted on the databases Web of Knowledge, PubMed and Scopus, using the terms "((Prader-Willi syndrome) OR (Prader Willi Syndrome)) AND ((psychosis) OR (psychotic illness))". All articles written in English and reporting original human research were reviewed. In all but three of the 16 cohort studies in which the genetic types were known, the authors reported higher rates of psychosis in people with PWS resulting from an mUPD, compared to those with the deletion subtype of PWS. When psychosis was present the presentation was psychosis similar regardless of genetic type and was usually characterised by an acute onset of hallucinations and delusions accompanied by confusion, anxiety and motor symptoms. CONCLUSIONS: The onset of confusion, an affective cyclical pattern with the presence of abnormal mental beliefs and experiences, usually of rapid onset is suggestive of the development of psychotic illness. Phenomenologically, this psychosis in people with PWS is atypical in comparison to schizophrenia and bipolar disorder in the general population. The relationship to psychosis in the general population and the optimum treatments remain uncertain.