The embodied cognition hypothesis suggests that motor and premotor areas are automatically and necessarily involved in understanding action language, as word conceptual representations are embodied. This transcranial magnetic stimulation (TMS) study explores the role of the left primary motor cortex in action-verb processing. TMS-induced motor-evoked potentials from right-hand muscles were recorded as a measure of M1 activity, while participants were asked either to judge explicitly whether a verb was action-related (semantic task) or to decide on the number of syllables in a verb (syllabic task). TMS was applied in three different experiments at 170, 350 and 500 ms post-stimulus during both tasks to identify when the enhancement of M1 activity occurred during word processing. The delays between stimulus onset and magnetic stimulation were consistent with electrophysiological studies, suggesting that word recognition can be differentiated into early (within 200 ms) and late (within 400 ms) lexical-semantic stages, and post-conceptual stages. Reaction times and accuracy were recorded to measure the extent to which the participants' linguistic performance was affected by the interference of TMS with M1 activity. No enhancement of M1 activity specific for action verbs was found at 170 and 350 ms post-stimulus, when lexical-semantic processes are presumed to occur (Experiments 1–2). When TMS was applied at 500 ms post-stimulus (Experiment 3), processing action verbs, compared with non-action verbs, increased the M1-activity in the semantic task and decreased it in the syllabic task. This effect was specific for hand-action verbs and was not observed for action-verbs related to other body parts. Neither accuracy nor RTs were affected by TMS. These findings suggest that the lexical-semantic processing of action verbs does not automatically activate the M1. This area seems to be rather involved in post-conceptual processing that follows the retrieval of motor representations, its activity being modulated (facilitated or inhibited), in a top-down manner, by the specific demand of the task.

Mental rotation (MR) is sustained by a network of brain regions, including parietal, pre-motor and primary motor (M1) cortices. However it is still not clear whether M1 is recruited only when individuals mentally rotate hands or whether it is also enhanced by MR of non-body parts. Here we report two experiments in which the involvement of M1 in MR of hands and letters was tested using TMS. In Experiments 1a and 1b participants were asked to judge whether two line drawings, depicting either hands or letters, were the same or mirror images of each other (N = 112). Subjects were presented with pairs of stimuli with the same orientation (baseline condition) in half of the trials, while in the other half the stimulus in the right visual field was rotated (rotation condition). They performed the same-different task in three experimental situations: TMS of the primary motor hand area delivered at 400 ms after stimulus onset, sham TMS, and no-TMS. We stimulated the left M1 in Experiment 1a, and the right in Experiment 1b. Results showed that in Experiment 1a participants were slower after TMS when they performed MR of hands but not of letters. In Experiment 1b we failed to find an effect of TMS on MR of hands and letters. While in Experiment 1 the stimulus to be rotated was always presented in the right visual field, in Experiment 2 it was presented either in the left or in the right visual field. Results showed that only when TMS was delivered to the left M1, participants' ability to mentally rotate right and left hands slowed down. Taken together, these findings suggest that the left but not the right M1 plays a critical role in MR of hands.

Recently, there has been increasing interest in techniques for enhancing working memory (WM), casting a new light on the classical picture of a rigid system. One reason is that WM performance has been associated with intelligence and reasoning, while its impairment showed correlations with cognitive deficits, hence the possibility of training it is highly appealing. However, results on WM changes following training are controversial, leaving it unclear whether it can really be potentiated. This study aims at assessing changes in WM performance by comparing it with and without training by a professional mnemonist. Two groups, experimental and control, participated in the study, organized in two phases. In the morning, both groups were familiarized with stimuli through an N-back task, and then attended a 2-hour lecture. For the experimental group, the lecture, given by the mnemonist, introduced memory encoding techniques; for the control group, it was a standard academic lecture about memory systems. In the afternoon, both groups were administered five tests, in which they had to remember the position of 16 items, when asked in random order. The results show much better performance in trained subjects, indicating the need to consider such possibility of enhancement, alongside general information-theoretic constraints, when theorizing about WM span.