Alessandro D'Ausilio

Encoding of human action in Broca's area.

Brocas area has been considered, for over a century, as the brain centre responsible for speech production. Modern neuroimaging and neuropsychological evidence have suggested a wider functional role is played by this area. In addition to the evidence that it is involved in syntactical analysis, mathematical calculation and music processing, it has recently been shown that Brocas area may play some role in language comprehension and, more generally, in understanding actions of other individuals. As shown by functional magnetic resonance imaging, Brocas area is one of the cortical areas activated by hand/mouth action observation and it has been proposed that it may form a crucial node of a human mirror-neuron system. If, on the one hand, neuroimaging studies use a correlational approach which cannot offer a final proof for such claims, available neuropsychological data fail to offer a conclusive demonstration for two main reasons: (i) they use tasks taxing both language and action systems; and (ii) they rarely consider the possibility that Brocas aphasics may also be affected by some form of apraxia. We administered a novel action comprehension test--with almost no linguistic requirements--on selected frontal aphasic patients lacking apraxic symptoms. Patients, as well as matched controls, were shown short movies of human actions or of physical events. Their task consisted of ordering, in a temporal sequence, four pictures taken from each movie and randomly presented on the computer screen. Patients performance showed a specific dissociation in their ability to re-order pictures of human actions (impaired) with respect to physical events (spared). Our study provides a demonstration that frontal aphasics, not affected by apraxia, are specifically impaired in their capability to correctly encode observed human actions.

Cross-modal plasticity of the motor cortex while listening to a rehearsed musical piece

Learning a musical piece requires the development of a strong linkage between sensory and motor representations. Audition plays a central role and a tight cortical auditory–motor corepresentation is a characteristic feature of music processing. Recent works have indicated the establishment of a functional connection between auditory and motor cortices during the learning of a novel piece, although no causal relation has yet been demonstrated. Here transcranial magnetic stimulation of the cortical motor representation involved in musical performance was used to test excitability changes in piano players during auditory presentation of a rehearsed and a non‐rehearsed piece. Results showed an increased motor excitability for the rehearsed but not for the non‐rehearsed piece. Moreover, we observed an increase of excitability over time as intracortical facilitation was already present after 30 min of training whereas cortico‐spinal facilitation increased after a longer training period (5 days).

Sensory-motor brain network connectivity for speech comprehension.

The act of listening to speech activates a large network of brain areas. In the present work, a novel data‐driven technique (the combination of independent component analysis and Granger causality) was used to extract brain network dynamics from an fMRI study of passive listening to Words, Pseudo‐Words, and Reverse‐played words. Using this method we show the functional connectivity modulations among classical language regions (Brocas and Wernickes areas) and inferior parietal, somatosensory, and motor areas and right cerebellum. Word listening elicited a compact pattern of connectivity within a parieto‐somato‐motor network and between the superior temporal and inferior frontal gyri. Pseudo‐Word stimuli induced activities similar to the Word condition, which were characterized by a highly recurrent connectivity pattern, mostly driven by the temporal lobe activity. Also the Reversed‐Word condition revealed an important influence of temporal cortices, but no integrated activity of the parieto‐somato‐motor network. In parallel, the right cerebellum lost its functional connection with motor areas, present in both Word and Pseudo‐Word listening. The inability of the participant to produce the Reversed‐Word stimuli also evidenced two separate networks: the first was driven by frontal areas and the right cerebellum toward somatosensory cortices; the second was triggered by temporal and parietal sites towards motor areas. Summing up, our results suggest that semantic content modulates the general compactness of network dynamics as well as the balance between frontal and temporal language areas in driving those dynamics. The degree of reproducibility of auditory speech material modulates the connectivity pattern within and toward somatosensory and motor areas. Hum Brain Mapp, 2010.

Sensorimotor communication in professional quartets

Non-verbal group dynamics are often opaque to a formal quantitative analysis of communication flow. In this context, ensemble musicians can be a reliable model of expert group coordination. In fact, bodily motion is a critical component of inter-musician coordination and thus could be used as a valuable index of sensorimotor communication. Here we measured head movement kinematics of an expert quartet of musicians and, by applying Granger Causality analysis, we numerically described the causality patterns between participants. We found a clear positive relationship between the amount of communication and complexity of the score segment. Furthermore, we also applied temporal and dynamical changes to the musical score, known by the first violin only. The perturbations were devised in order to force unidirectional communication between the leader of the quartet and the other participants. Results show that in these situations, unidirectional influence from the leader decreased, thus implying that effective leadership may require prior sharing of information between participants. In conclusion, we could measure the amount of information flow and sensorimotor group dynamics suggesting that the fabric of leadership is not built upon exclusive information knowledge but rather on sharing it.

A theory for how sensorimotor skills are learned and retained in noisy and nonstationary neural circuits

Significance The synaptic trace theory of memory posits that the brain retains information through learning-induced changes in synaptic connections. Once consolidated, a memory is embodied through its fixed trace. For the case of motor memories, e.g., learning how to ride a bicycle, we propose a slight variation on this theme. Because there are so many different ways for the motor system to accomplish the same task goal, motor memories are defined not by fixed patterns of synaptic connections, but rather by nonstationary patterns that fluctuate coherently while still generating the same fixed input–output mapping. This mechanism provides a noisy sensorimotor system with enough flexibility so that motor learning can occur rapidly with respect to new memories without overwriting older memories. During the process of skill learning, synaptic connections in our brains are modified to form motor memories of learned sensorimotor acts. The more plastic the adult brain is, the easier it is to learn new skills or adapt to neurological injury. However, if the brain is too plastic and the pattern of synaptic connectivity is constantly changing, new memories will overwrite old memories, and learning becomes unstable. This trade-off is known as the stability–plasticity dilemma. Here a theory of sensorimotor learning and memory is developed whereby synaptic strengths are perpetually fluctuating without causing instability in motor memory recall, as long as the underlying neural networks are sufficiently noisy and massively redundant. The theory implies two distinct stages of learning—preasymptotic and postasymptotic—because once the error drops to a level comparable to that of the noise-induced error, further error reduction requires altered network dynamics. A key behavioral prediction derived from this analysis is tested in a visuomotor adaptation experiment, and the resultant learning curves are modeled with a nonstationary neural network. Next, the theory is used to model two-photon microscopy data that show, in animals, high rates of dendritic spine turnover, even in the absence of overt behavioral learning. Finally, the theory predicts enhanced task selectivity in the responses of individual motor cortical neurons as the level of task expertise increases. From these considerations, a unique interpretation of sensorimotor memory is proposed—memories are defined not by fixed patterns of synaptic weights but, rather, by nonstationary synaptic patterns that fluctuate coherently.

Lexicality drives audio-motor transformations in Broca's area

Brocas area is classically associated with speech production. Recently, Brocas area has also been implicated in speech perception and non-linguistic information processing. With respect to the latter function, Brocas area is considered to be a central area in a network constituting the human mirror system, which maps observed or heard actions onto motor programs to execute analogous actions. These mechanisms share some similarities with Libermans motor theory, where objects of speech perception correspond to listeners intended articulatory gestures. The aim of the current series of behavioral, TMS and fMRI studies was to test if Brocas area is indeed implicated in such audio-motor transformations. More specifically, using a classical phonological rhyme priming paradigm, we investigated whether the role of Brocas area could be purely phonological or rather, is lexical in nature. In the behavioral baseline study, we found a large priming effect in word prime/target pairs (W-W) and no effect for pseudo-words (PW-PW). Online TMS interference of Brocas area canceled the priming difference between W-W and PW-PW by enhancing the effects for PW-PW. Finally, the fMRI study showed activation of Brocas area for W-W pairs, but not for PW-PW pairs. Our data show that Brocas area plays a significant role in speech perception strongly linked to the lexicality of a stimulus.

Listening to speech recruits specific tongue motor synergies as revealed by transcranial magnetic stimulation and tissue-Doppler ultrasound imaging

The activation of listeners motor system during speech processing was first demonstrated by the enhancement of electromyographic tongue potentials as evoked by single-pulse transcranial magnetic stimulation (TMS) over tongue motor cortex. This technique is, however, technically challenging and enables only a rather coarse measurement of this motor mirroring. Here, we applied TMS to listeners’ tongue motor area in association with ultrasound tissue Doppler imaging to describe fine-grained tongue kinematic synergies evoked by passive listening to speech. Subjects listened to syllables requiring different patterns of dorso-ventral and antero-posterior movements (/ki/, /ko/, /ti/, /to/). Results show that passive listening to speech sounds evokes a pattern of motor synergies mirroring those occurring during speech production. Moreover, mirror motor synergies were more evident in those subjects showing good performances in discriminating speech in noise demonstrating a role of the speech-related mirror system in feed-forward processing the speakers ongoing motor plan.

Mirror-Like Mechanisms and Music

The neural processes underlying sensory-motor integration have always attracted strong interest. The classic view is that action and perception are two extremes of mental operations. In the past 2 decades, though, a large number of discoveries have indeed refuted such an interpretation in favor of a more integrated view. Specifically, the discovery of mirror neurons in monkey premotor cortex is a rather strong demonstration that sensory and motor processes share the same neural substrates. In fact, these cells show complex sensory-motor properties, such that observed, heard, or executed goal-directed actions could equally activate these neurons. On the other hand, the neuroscience of music has similarly emerged as an active and productive field of research. In fact, music-related behaviors are a useful model of action-perception mechanisms and how they develop through training. More recently, these two lines of research have begun to intersect into a novel branch of research. As a consequence, it has been proposed recently that mirror-like mechanisms might be at the basis of human music perception-production abilities. The scope of the present short review is to set the scientific background for mirror-like mechanisms in music by examining recent published data.

Motor excitability evaluation in developmental stuttering: a transcranial magnetic stimulation study.

INTRODUCTION Developmental stuttering (DS) is viewed as a motor speech-specific disorder, although several lines of research suggest that DS is a symptom of a broader motor disorder. We investigated corticospinal excitability in adult DS and normal speakers. METHODS Transcranial magnetic stimulation (TMS) was administered over left/right hand representation of the motor cortex while recording motor evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI) muscle. Resting, active motor thresholds, silent period threshold and duration were measured. A stimulus-response curve at resting was also obtained to evaluate MEP amplitudes. RESULTS Lower corticospinal responses in the left hemisphere of DS were found, as indicated by a reduction of peak-to-peak MEP amplitudes compared to normal speakers. CONCLUSIONS This provides further evidence that DS may be a general motor deficit that also involves motor non-speech-related structures. Moreover, our results confirm that DS may be related to left hemisphere hypoactivation and/or lower left hemisphere dominance. The present data and protocol may be useful for diagnosis of subtypes of DS that may benefit from pharmacological treatment by targeting the general level of cortical excitability.

Why Professional Athletes Need a Prolonged Period of Warm-Up and Other Peculiarities of Human Motor Learning

ABSTRACT Professional athletes involved in sports that require the execution of fine motor skills must practice for a considerable length of time before competing in an event. Why is such practice necessary? Is it merely to warm-up the muscles, tendons, and ligaments, or does the athletes sensorimotor network need to be constantly recalibrated? In this article, the authors present a point of view in which the human sensorimotor system is characterized by: (a) a high noise level and (b) a high learning rate at the synaptic level (which, because of the noise, does not equate to a high learning rate at the behavioral level). They argue that many heuristics of human skill learning, including the need for a prolonged period of warm-up in experts, follow from these assumptions.