Recent evidence in healthy participants suggests that a motor subcomponent of working memory (mWM) may exist. We investigated whether this mWM is impaired in patients with a motor-dominant left hemisphere (LH) stroke and apraxia. Furthermore, we hypothesized that a deficient mWM contributes to deficits in motor cognition, that is, apraxia, in LH stroke. The study included 52 patients with LH stroke and 25 age-matched controls. Patients were classified into LH stroke patients with and without apraxia based on deficits in gesture imitation and object use. All participants were examined using the block span test (visuospatial WM), the digit span test (verbal WM), and a novel mWM task. In the latter, participants were presented with static pictures depicting three different actions: actions with objects, meaningless actions, and meaningful actions. In the mWM task, LH stroke patients with apraxia performed worse than age-matched controls. Notably, LH stroke patients with apraxia showed more pronounced mWM deficits than those without apraxia. These results remained significant even after controlling for visuospatial and verbal WM deficits. Regression analyses revealed that LH stroke patients' mWM deficits predicted deficits in imitation. Data provide neuropsychological evidence for a motor subsystem of WM and suggest that deficits in mWM contribute to the severity of apraxia in LH stroke patients.

Action understanding and learning are suggested to be mediated, at least in part, by the human mirror neuron system (hMNS). Static images as well as videos of actions with the outcome occluded have been shown to activate the hMNS. However, whether the hMNS preferentially responds to end or means of an action remains to be investigated. We, therefore, presented subjects with videos of intentional actions that were shown from two perspectives (factor 1, perspective: first vs. third person) while subjects directed their attention to the means or the end thereof (factor 2, task: means vs. end). End- or means-related changes in BOLD signal and corticospinal excitability (CSE) were assessed using fMRI and TMS, respectively. Judging the means of an action compared with its end differentially activated bilateral ventral premotor (vPMC) and inferior parietal cortex (IPL), that is, the core regions of the hMNS. The reverse contrast revealed left precuneus and bilateral superior frontal, angular, and middle temporal gyrus activity. In accordance, the two tasks, although identically in stimulus properties, modulated CSE differentially. Although recent studies suggest that the hMNS may prefer the presence of a goal or context, our data show that within the same context, it responds preferentially when attention is directed to the action means . Consequently, in addition to inferring action goals, a key function of the hMNS may be to anticipate the trajectories and dynamics of observed actions, which is a prerequisite for any timely interaction.