Interpretation of mentalistic actions and sarcastic remarks: effects of frontal and posterior lesions on mentalising.

Recent work has linked mentalising ability to ventromedial frontal brain regions, the temporal poles and the temporo-parietal junction. The present study set out to examine the performance of participants with focal frontal and posterior lesions and a matched healthy control group on mentalising tasks with different types of pragmatic materials. Four types of materials were used: control physical events, human actions, and direct and indirect sarcastic remarks. Ability to interpret these was tested by asking participants both to explain the events, actions or remarks, and then to choose the best solution from four alternatives presented. Those with frontal lesions were impaired in comprehension of each of the sets of mentalistic materials, but were intact in comprehension of the control non-mentalistic items. There was some evidence linking the generation of free responses for the mentalistic materials to lateral frontal regions; this may be mediated by executive skills. There was also evidence linking selection amongst alternative solutions to right frontal regions, particularly ventromedial areas. There was little evidence that posterior regions played any significant part, at least for the present mentalistic materials. Errors in sarcasm comprehension made by participants with frontal lesions revealed that these were not always literal in nature, suggesting two separable components in comprehension: appreciating that a meaning is not intended literally, and understanding the specific meaning in the social context.

Parietal updating of limb posture: an event-related fMRI study.

The posterior parietal cortex (PPC) is thought to integrate different kinds of sensory information (e.g., visual, auditory, somatosensory) to produce multiple representations of space that are each associated with different types or combinations of action; such as saccadic eye movements and reaching or grasping movements of the upper limb. Lesion studies in monkeys and in humans have shown that reaching movements to visually defined and to posturally defined targets can be dissociated from one another; indicating that different regions of the parietal cortex may code the same movement in either extrinsic (visual) or intrinsic (postural) coordinates. These studies also suggest that regions within the posterior parietal cortex play an important role in maintaining an accurate and up-to-date representation of the current postural state of the body (the body schema). We used event-related functional magnetic resonance imaging (fMRI) to investigate those brain areas involved in maintaining and updating postural (i.e., non-visual) representations of the upper limb that participate in the accurate control of reaching movements. We show that a change in the posture of the upper-limb is associated with a significant increase in BOLD activation in only one brain region--the superior parietal cortex, particularly the medial aspect (precuneus). We note that this finding is consistent with the suggestion, based upon human neurological investigations and monkey electrophysiology, that this region of the PPC may participate in the dynamic representation of the body schema, and is the most likely location for damage leading to errors in visually guided reaching to non-foveated target locations. We also note that this brain area corresponds to a region of PPC recently identified as the human homologue of the Parietal Reach Region (PRR) observed in the monkey brain that has been thought to represent reaching movements in eye-centred coordinates.

Social cognition after head injury: sarcasm and theory of mind.

Closed head injury (CHI) is associated with communication difficulties in everyday social interactions. Previous work has reported impaired comprehension of sarcasm, using sarcastic remarks where the intended meaning is the opposite of the sincere or literal meaning. Participants with CHI in the present study were assessed using two types of sarcastic items, those with a directly opposite meaning and those with an indirect, non-literal but not directly opposite meaning. The CHI group was differentially poorer at comprehending sarcastic versus sincere remarks, although type of sarcastic materials did not influence performance. Errors involved not only literal interpretations, but also incorrect non-literal interpretations. Theory of mind (mentalising) was also assessed by comparing comprehension of human actions with control physical events. The CHI group was selectively impaired on the mentalising component of this task, and mentalising scores correlated with sarcasm comprehension. The implications of the findings for our understanding of impaired sarcastic comprehension after acquired brain injury are discussed.