Please cite this article in press as: R. Wood, et al., Visuotactile empathy within the primary somatosensory cortex revealed by short-latency afferent inhibition, Neurosci. Lett. (2010), doi:10.1016/j.neulet.2010.02.012 ARTICLE IN PRESS UNCORRECTED PROOF G Model NSL 26827 1–4 Neuroscience Letters xxx (2010) xxx–xxx 1 Contents lists available at ScienceDirect Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet Visuotactile empathy within the primary somatosensory cortex revealed by short-latency afferent inhibition 1 2 Rachel Wood a , Vittorio Gallese a,c , Luigi Cattaneo b,∗ 3 a Dipartimento di Neuroscienze, Università di Parma, Parma, Italy 4 b Centro Interdipartmentale Mente/Cervello, Università di Trento, 38100 Mattarello (Trento), Via delle Regole 101, 38123 Trento, Italy Q1 5 c IIT, Italian Institute of Technology, Section of Parma, Parma, Italy 6 7 article info 8 9 Article history: 10 Received 26 November 2009 11 Received in revised form 4 February 2010 12 Accepted 5 February 2010 13 14 Keywords: 15 Empathy 16 Touch 17 Short-latency afferent inhibition Q2 18 Mirror 19 Transcranial magnetic 20 Stimulation 21 Embodiment 22 abstract Intersubjectivity entails the taking of another’s perspective in order to understand their experience of the world. This perspective taking capacity extends to the intra-individual sharing of tactile experience. Previous studies have shown modulation of motor cortex excitability in response to the observation of aversive tactile stimulation to the hand of another person. Here we used transcranial magnetic stimulation (TMS) and peripheral stimulation to induce a short-latency afferent inhibition (SAI) effect, which we then sought to modulate via observation of non-noxious tactile stimulation to the hand of a model. Side congruency between the observed (model) and the recorded (participant) hand induced an increase of SAI and this effect was found to hold for motor-evoked potentials (MEPs) recorded from both left and right hands. Inhibition was not found with MEPs evoked using unconditioned pulses of TMS. These results demonstrate a sensorimotor response to observed non-noxious stimulation and suggest an empathic matching system for the tactile experiences of others. © 2010 Published by Elsevier Ireland Ltd. Intersubjectivity requires shared experience and the capacity to 23 take others’ perspectives. A number of studies have demonstrated 24 that the neural structures underlying sensation processing are 25 recruited when observing the sensory experiences of others. fMRI 26 studies of the effects of touch observation [3,9,11] found activation 27 of secondary or primary somatosensory cortex when participants 28 experienced touch and when they observed another person or 29 object being touched. These findings support the notion of shared 30 neural circuits for first and third person experiences of touch. This 31 direct matching mechanism bears strong analogies with the mir- 32 ror systems, where observation of an action automatically activates 33 parts of corresponding neural circuits in the observer, neural cir- 34 cuits that would be recruited if she were performing the action 35 herself [7,10]. 36 Visual activation of somatosensory cortical circuits for touch 37 observation occurs regardless of the animacy of the entity being 38 touched (i.e. object or person), is independent of the observer’s 39 perspective (i.e. ego- or allo-centric) and is not restricted to the 40 domain of intentional touch [9]. This suggests that the observation 41 of any touch can activate shared somatosensory circuits, although 42 intentional touches appear to elicit a greater response in SI (BA 43 2) than accidental touches. Visuotactile mirroring may thus pro- 44 vide an embodied mechanism to support the interpretation of any 45 ∗ Corresponding author. E-mail address: luigi.cattaneo@unitn.it (L. Cattaneo). touch (regardless of animacy or intentionality) via processes of 46 multimodal integration. 47 Aside from empathy for touch, some studies have addressed 48 the issue of empathy for somatosensory sensation that carries a 49 much stronger affective implication: cutaneous pain. Avenanti et 50 al. [1] were able to demonstrate modulation of sensorimotor activ- 51 ity in response to pain observation using a single-pulse transcranial 52 magnetic stimulation (TMS) paradigm. Motor-evoked potentials in 53 the muscle participants saw being subjected to painful stimulation 54 were significantly reduced. Inhibition was correlated to the inten- 55 sity of the pain observed but not to task instructions, indicating that 56 the sensorimotor component of empathy for pain may be stimulus 57 driven, i.e., predicated on the perceived intensity of the aversive 58 stimulation received by the observed other [1]. 59 Observation of touch is known to elicit both perceptual and neu- 60 rophysiological changes in the observer [4,14–16]. The observation 61 of painful stimulation has been shown to produce a motor response 62 in the observer, however this effect has not previously been found 63 for non-painful stimuli. Thus, we used a short-latency afferent inhi- 64 bition (SAI) paradigm [17] to test the primary sensory and motor 65 cortices for an effect analogous with that found for noxious touch 66 during the observation of non-noxious touch. 67 The SAI technique tests the effects of an afferent somatosen- 68 sory stimulus on the excitability of the motor cortex. TMS alone 69 at stimulation intensities just above motor threshold is capable of 70 probing the excitability state of the motor cortex by depolarizing 71 cortical interneurons and ultimately exciting corticospinal neurons 72 0304-3940/$ – see front matter © 2010 Published by Elsevier Ireland Ltd. doi:10.1016/j.neulet.2010.02.012