Differential demands on working memory for guiding a simple action sequence: Evidence from closed-head-injured subjects

In the present study, a working memory paradigm was used to assess coordinative abilities required for the flexible control of a sequence of actions. Subjects had to maintain and recall a list of digits that functioned as an ensemble of activity cues used for guiding a sequence of forced-choice responses. In three task conditions, the demand on the selection of the activity cues was varied parametrically to manipulate the requirement of coordinating maintenance and processing operations of working memory for guiding the response sequences. A comparison between subjects suffering from severe closed head injury (CHI) and matched controls in a blocked presentation of task conditions revealed that patients, in contrast to controls, did not preplan the sequence by rearranging the ensemble of activity cues prior to execution of the action sequence. Patients' performance was more comparable to controls tested in a random presentation in which preplanning was not possible. Our results further suggest that patients are less efficient in selecting activity cues from working memory, especially in more demanding situations when activity cues have to be completely reordered for guiding a sequence of actions. These results point to an executive dysfunction in CHI subjects that may contribute to the deficits known as inflexible and rigid behavior