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 coordina tive 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 resp onses. In three task conditions, the demand on the selection of the activit y cues was varied parametrically to manipulate the requirement of coordinat ing maintenance and processing operations of working memory for guiding the response sequences. A comparison between subjects suffering from severe cl osed head injury (CHI) and matched controls in a blocked presentation of ta sk conditions revealed that patients, in contrast to controls, did not prep lan the sequence by rearranging the ensemble of activity cues prior to exec ution of the action sequence. Patients' performance was more comparable to controls tested in a random presentation in which preplanning was not possi ble. Our results further suggest that patients are less efficient in select ing activity cues from working memory, especially in more demanding situati ons when activity cues have to be completely reordered for guiding a sequen ce of actions. These results point to an executive dysfunction in CHI subje cts that may contribute to the deficits known as inflexible and rigid behav ior.