Attributing a meaning to hand movements: an fMRI study

Increasing attention is being paid to functional activations related to body movement inner representations, during either observation or imagery (1,2). So far, however, few studies have dealt with the presence or absence of a meaning in the observed and/or imagined movements (3).MethodsThirteen healthy right-handed volunteers (5 males, 8 females; age 20-31) took part in the study. At the beginning of each trial, a short video was presented, showing different kinds of intransitive hand movements: pantomimes, or symbolic gestures, or nonsense movements. The subjects had either to imagine to perform the same movement they had just seen in the previous video (imagery task); or to observe another movement, different from the previous one (observation task). Four runs, twenty trials each, were carried out for each subject. Functional imaging was performed on a 1.5 Signa GE MR scanner, acquiring 18 contiguous axial slices (TR: 2000 ms; voxel size: 3.75x3.75x6 mm). Data analysis was carried out using the SPM99 package (Wellcome Department of Imaging Neuroscience, London, UK). Multi-subject analyses were performed using a random effect model. In particular, in order to identify patterns of activation related to the attribution of a meaning to movements, we performed a conjunction analysis of the contrasts “pantomimes vs. nonsense” and “symbolic vs. nonsense”, for observation and imagery separately.ResultsDuring the observation of meaningful actions, as compared with meaningless movements, mainly left hemisphere activations (Fig. 1A) were found in the frontal and temporal cortex: namely, in precentral gyrus (BA 6), inferior frontal gyrus (IFG, BA45) and middle frontal gyrus (BA10), and in superior temporal gyrus (BA22); in addition, activity increased in the right middle temporal gyrus and in medial occipital areas bilaterally. During imagery of meaningful vs. meaningless movements, regions of increased signal were in the left IFG (BA45) (Fig 1B), in the right parietal operculum/posterior insula, and in lateral occipital/posterior temporal cortex in both hemispheres.ConclusionsA common region functionally activated during both imagery and observation of meaningful vs. meaningless movements is the left IFG. Actually, a smaller signal increase was present in IFG also for meaningless movements (data not shown). The IFG had been found active in a previous study when observing meaningful upper limb movements with the intention to either recognize or to imitate them (3). The IFG is part of the so-called mirror system, devoted to action understanding and imitation (1). Our results support the hypothesis that the left IFG is specifically involved in attributing a meaning to upper limb movements, during both passive (observation) and active (imagery) inner representations. 1) G. Rizzolatti and L. Craighero Annu.Rev.Neurosci. 2004.2) M. Jeannerod Neuroimage. 14:S103-S109, 2001.3) J. Decety et al. Brain 120:1763-1777, 1997.