Luigi Cattaneo

Impairment of actions chains in autism and its possible role in intention understanding.

Experiments in monkeys demonstrated that many parietal and premotor neurons coding a specific motor act (e.g., grasping) show a markedly different activation when this act is part of actions that have different goals (e.g., grasping for eating vs. grasping for placing). Many of these “action-constrained” neurons have mirror properties firing selectively to the observation of the initial motor act of the actions to which they belong motorically. By activating a specific action chain from its very outset, this mechanism allows the observers to have an internal copy of the whole action before its execution, thus enabling them to understand directly the agents intention. Using electromyographic recordings, we show that a similar chained organization exists in typically developing children, whereas it is impaired in children with autism. We propose that, as a consequence of this functional impairment, high-functioning autistic children may understand the intentions of others cognitively but lack the mechanism for understanding them experientially.

Processing abstract language modulates motor system activity

Embodiment theory proposes that neural systems for perception and action are also engaged during language comprehension. Previous neuroimaging and neurophysiological studies have only been able to demonstrate modulation of action systems during comprehension of concrete language. We provide neurophysiological evidence for modulation of motor system activity during the comprehension of both concrete and abstract language. In Experiment 1, when the described direction of object transfer or information transfer (e.g., away from the reader to another) matched the literal direction of a hand movement used to make a response, speed of responding was faster than when the two directions mismatched (an action–sentence compatibility effect). In Experiment 2, we used single-pulse transcranial magnetic stimulation to study changes in the corticospinal motor pathways to hand muscles while reading the same sentences. Relative to sentences that do not describe transfer, there is greater modulation of activity in the hand muscles when reading sentences describing transfer of both concrete objects and abstract information. These findings are discussed in relation to the human mirror neuron system.

Use-induced motor plasticity affects the processing of abstract and concrete language

Summary Traditional analyses of language [1] emphasize an arbitrary correspondence between linguistic symbols and their extensions in the world, but recent behavioral and neurophysiological [2,3] studies have demonstrated a processing link between a symbol and its extension: that is, comprehension of language about concrete events relies in part on a simulation process that calls on neural systems used in perceiving and acting on those extensions. It is an open question, however, whether this simulation process is necessary for abstract language understanding [4,5]. Here we report how, using a new technique based on use-induced neural plasticity [6], we have obtained evidence for a causal link between the motor system and the comprehension of both concrete and abstract language.

State-Dependent TMS Reveals a Hierarchical Representation of Observed Acts in the Temporal, Parietal, and Premotor Cortices

A transcranial magnetic stimulation (TMS) adaptation paradigm was used to investigate the neural representation of observed motor behavior in the inferior parietal lobule (IPL), ventral premotor cortex (PMv), and in the cortex around the superior temporal sulcus (STS). Participants were shown adapting movies of a hand or a foot acting on different objects and were asked to compare to the movie, a motor act shown in test pictures. The invariant features between adapting and test stimuli fitted a 2 x 2 design: same or different action made by the same or different effector. Neuronavigated TMS pulses were delivered at the onset of each test picture. TMS over the left and right PMv and over the left IPL induced a selective shortening of reaction times (RTs) to stimuli showing a repeated (adapted) action, regardless of the effector performing it. In a second experiment, TMS applied over the left STS induced shortening of RTs for adapted actions but only if also the effector was repeated. The results indicate that observed motor behavior is encoded with the body part that performs it in the temporal lobe. A hierarchically higher level of representation is carried by neural populations in the parietofrontal regions, where acts are encoded in an abstract way.

Planning actions in autism

It has been suggested that the deficit in understanding others’ intention in autism depends on a malfunctioning of the mirror system. This malfunction could be due either to a deficit of the basic mirror mechanism or to a disorganization of chained action organization on which the mirror understanding of others’ intention is based. Here we tested this last hypothesis investigating the kinematics of intentional actions. Children with autism and typically developing children (TD) were asked to execute two actions consisting each of three motor acts: the first was identical in both actions while the last varied for its difficulty. The result showed that, unlike in TD children, in children with autism the kinematics of the first motor act was not modulated by the task difficulty. This finding strongly supports the notion that children with autism have a deficit in chaining motor acts into a global action.

Representation of Goal and Movements without Overt Motor Behavior in the Human Motor Cortex: A Transcranial Magnetic Stimulation Study

We recorded motor-evoked potentials (MEPs) to transcranial magnetic stimulation from the right opponens pollicis (OP) muscle while participants observed an experimenter operating two types of pliers: pliers opened by the extension of the fingers and closed by their flexion (“normal pliers”) and pliers opened by the flexion of the fingers and closed by their extension (“reverse pliers”). In one experimental condition, the experimenter merely opened and closed the pliers; in the other, he grasped an object with them. In a further condition, the participants imagined themselves operating the normal and reverse pliers. During the observation of actions devoid of a goal, the MEP amplitudes, regardless of pliers used, reflected the muscular pattern involved in the execution of the observed action. In contrast, during the observation of goal-directed actions, the MEPs from OP were modulated by the action goal, increasing during goal achievement despite the opposite hand movements necessary to obtain it. During motor imagery, the MEPs recorded from OP reflected the muscular pattern required to perform the imagined action. We propose that covert activity in the human motor cortex may reflect different aspects of motor behavior. Imagining oneself performing tool actions or observing tool actions devoid of a goal activates the representation of the hand movements that correspond to the observed ones. In contrast, the observation of tool actions with a goal incorporates the distal part of the tool in the observers body schema, resulting in a higher-order representation of the meaning of the motor act.

Numbers within Our Hands: Modulation of Corticospinal Excitability of Hand Muscles during Numerical Judgment

Developmental and cross-cultural studies show that finger counting represents one of the basic number learning strategies. However, despite the ubiquity of such an embodied strategy, the issue of whether there is a neural link between numbers and fingers in adult, literate individuals remains debated. Here, we used transcranial magnetic stimulation to study changes of excitability of hand muscles of individuals performing a visual parity judgment task, a task not requiring counting, on Arabic numerals from 1 to 9. Although no modulation was observed for the left hand muscles, an increase in amplitude of motor-evoked potentials was found for the right hand muscles. This increase was specific for smaller numbers (1 to 4) as compared to larger numbers (6 to 9). These findings indicate a close relationship between hand/finger and numerical representations.

Peripheral neuropathy in Wegener’s granulomatosis, Churg–Strauss syndrome and microscopic polyangiitis

Objective: To compare the clinical aspects of peripheral neuropathy associated with Wegener’s granulomatosis (WG), Churg–Strauss syndrome (CSS) and microscopic polyangiitis (MP). Methods: Cohort study conducted in a single university hospital. Patients were included when a definite diagnosis of WG, CSS or MP was made according to the current classification criteria in our hospital, between 1999 and 2006. All patients underwent periodically clinical and electrophysiological screening for peripheral neuropathy, assessment of disability, and clinical and laboratory evaluation during a mean follow-up of 38 months. Results: Sixty-four consecutive patients diagnosed with WG (26 patients), CSS (26 patients) and MP (12 patients) were recruited. Peripheral neuropathy occurred in 27/64 patients: six with WG, 15 with CSS and six with MP. Neuropathy occurred earlier in the disease history in CSS and MP compared with WG. Among patients with WG, those who developed peripheral neuropathy during follow-up were older than those without neuropathy both at the time of onset and of diagnosis of vasculitis. Distal symmetric polyneuropathy was present in 11 patients, and single or multiple mononeuropathy in 16. Patients with WG had a less severe form of mononeuritis multiplex than CSS or MPA patients. Disability and pain were greater in patients with mononeuropathy, although one-third of them were painless. Relapses of neuropathy were extremely infrequent. Conclusions: Peripheral neuropathy in WG occurs less frequently, later in the disease course and in a milder form than in CSS and MP. Single or multiple mononeuropathy associated with these subsets of vasculitis can often be painless.

Covert Speech Arrest Induced by rTMS over Both Motor and Nonmotor Left Hemisphere Frontal Sites

Blocking the capacity to speak aloud (overt speech arrest, SA) may be induced by repetitive transcranial magnetic stimulation (rTMS). The possibility, however, of blocking internal speech (covert SA) has not been explored. To investigate this issue, we conducted two rTMS experiments. In the first experiment, we stimulated two left frontal lobe sites. The first was a motor site (left posterior site) and the second was a nonmotor site located in correspondence to the posterior part of the inferior frontal gyrus (IFG) (left anterior site). The corresponding right hemisphere nonmotor SA site was stimulated as a control. In the second experiment, we focused on the right hemisphere and stimulated a right hemisphere motor site (right posterior site), and, as control sites, a right hemisphere nonmotor site corresponding to the IFG (right anterior site) and a left hemisphere anteromedial site (left control). For both experiments, participants performed a syllable counting task both covertly and overtly for each stimulation site. Longer latencies in this task imply the occurrence of an overt and/or covert SA. All participants showed significantly longer latencies when stimulation was either over the left posterior or the left anterior site, as compared with the right hemisphere site (Experiment 1). This result was observed for the overt and covert speech task alike. During stimulation of the posterior right hemisphere site, a dissociation for overt and covert speech was observed. An overt SA was observed but there was no evidence for a covert SA (Experiment 2). Taken together, the results show that rTMS can induce a covert SA when applied to areas over the brain that are pertinent to language. Furthermore, both the left posterior/motor site and the left anterior/IFG site appear to be essential to language elaboration even when motor output is not required.

Excitability of human motor cortex inputs prior to grasp

Transcranial magnetic stimulation (TMS) was used to investigate corticospinal excitability during the preparation period preceding visually guided self‐paced grasping. Previously we have shown that while subjects prepare to grasp a visible object, paired‐pulse TMS at a specific interval facilitates motor‐evoked potentials (MEPs) in hand muscles in a manner that varies with the role of the muscle in shaping the hand for the upcoming grasp. This anticipatory modulation may reflect transmission of inputs to human primary motor cortex (M1) for visuomotor guidance of hand shape. Conversely, single‐pulse TMS is known to suppress MEPs during movement preparation. Here we investigate the time course of single‐ and paired‐pulse MEP modulation. TMS was delivered over M1, at different time intervals after visual presentation of either a handle or a disc to healthy subjects. Participants were instructed to view the object, and later to grasp it when given a cue. During grasp there was a specific pattern of hand muscle activity according to the object grasped. MEPs were evoked in these muscles by TMS delivered prior to grasp. Paired‐pulse MEPs were facilitated, whilst single‐pulse MEPs were suppressed. The pattern of facilitation matched the object‐specific pattern of muscle activity for TMS pulses delivered 150 ms or more after object presentation. However, this effect was not present when TMS was delivered immediately after object presentation, or if the delivery of TMS was given separately from the cue to perform the grasp action. These results suggest that object‐related information for preparation of appropriate hand shapes reaches M1 only immediately preceding execution of the grasp.