SRT lengthening: role of an alertness deficit in frontal damaged patients

Numerous studies have documented the lengthening of reaction time (RT) following brain damage. However, the origin of response retardation and its anatomical basis still remain unknown. This study assessed simple RT (SRT) and choice RT (CRT) in patients with frontal or posterior damage. It showed (i) that RTs were longer in frontal damaged patients; (ii) with a constant response retardation across SRT and CRT tests; (iii) that minimum and percentile 25th SRTs of the frontal group were within normal ranges, indicating that they were able to produce fast responses; (iv) that percentiles 50 and 75th SRTs of the frontal group were longer, indicating that they produced a lower proportion of fast responses; (v) an interpretation supported by the decrement of the peak of SRT distribution. Such a pattern is highly suggestive of a disorder of an attentional process required to trigger the same response as fast as possible throughout the test. According to Posner's model of attention, this function is devoted to the alerting network and the present study supports the key role of the frontal lobes for alertness.