Evaluation of the supervisory system in elderly subjects with and without disinhibition

Disinhibition and irritability, defined as loss of behavioral and emotional control, are frequent in the elderly. The working hypothesis for this study was that these disorders are associated with a cognitive alteration of control processes that manifests as non-routine behavior because of the dysfunction of a general executive component known as the supervisory attentional system (SAS).

A total of 28 elderly subjects with mild cognitive impairment were recruited and divided into two groups using the Neuropsychiatric Inventory. Fourteen subjects were allocated to the disinhibited group and 14 subjects matched for age, sex and educational level formed a disinhibition-free control group. The neuropsychological battery included the following tests: Mini Mental Score Evaluation, Boston Naming test, Token test, Trail Making and Verbal Fluency. Two tasks were specifically designed to stress the SAS: 1) A specific verbal sentence arrangement task in which subjects had to use sequential reasoning with verbal material. Each test sequence consisted of a series of words shown in jumbled order. The construction of some sequences had to be done by using familiar routine associations (valid conditions). In contrast, other sequences required the overriding selection of familiar routine associations, which were inappropriate within the general context of the task (invalid conditions). 2) Using the Continuous Performance Test, four aspects were evaluated: sustained, selective, preparation and suppressive attention.

The only group differences in neuropsychological test results were the following: 1) the sentence arrangement task. In comparison with the control group, the disinhibited group was impaired in invalid conditions and the calculated difference between the number of correct responses in invalid conditions minus that in valid conditions was significantly higher; and 2) the CPT. Disinhibited subjects had a significantly lower number of hits, exclusively in the 'suppressive attention' paradigm. These results suggest that subjects with disinhibition have impaired supervisory system function.