Journal of the Neurological Sciences 174 (2000) 122–126 www.elsevier.com / locate / jns Magnetic stimulation study during observation of motor tasks a, a b a a * Filippo Brighina , Vincenzo La Bua , Massimiliano Oliveri , Aurelio Piazza , Brigida Fierro a ` Istituto di Neuropsichiatria, Universita di Palermo, Via G. La Loggia, 1, 90129 Palermo, Italy b IRCSS S. Lucia, Rome, Italy Received 6 January 1999; received in revised form 4 January 2000; accepted 6 January 2000 Abstract The aim of the study was to assess if the observation of single or more complex muscle movements activates the premotor cortex in man. We stimulated by transcranial magnetic stimulation the right and left motor cortex recording from the abductor pollicis brevis of eight normal subjects, during observation of different movements performed by the examiner: (1) single movements: thumb abduction, arm elevation; (2) motor sequences: finger opposing movements performed in an ordinate sequence: 1–2, 1–3, 1–4, 1–5, 1–2 . . . , and in a non-consecutive non-repetitive order: 1–3, 1–5, 1–4, 1–2, 1–5, 1–2 . . . We found an increased excitability of the right cortex during observation of isolated muscle movement regardless of which muscle is moved. At the stimulation of the left cortex, MEPs were significantly increased during observation of complex muscular synergies.  2000 Elsevier Science B.V. All rights reserved. Keywords: Transcranial magnetic stimulation; Motor task observation; MEP facilitation 1. Introduction potentials (MEPs) during observation of projective hand movements toward targets in extrapersonal space. Neurophysiological studies in experimental monkey The aim of our study was to assess by TMS if the demonstrated that neurons in premotor area F5 discharge observation of meaningless voluntary movements executed during goal-directed movements such as grasping, man- in intra-personal space [8] is able to facilitate neurons ipulating, holding and tearing [1,2]. It has been also normally active during the execution of the movement. demonstrated that a particular subset of F5 neurons: Additional purposes were to investigate if: (i) the facilitat- ‘mirror neurons’ in monkey are activated not only by ory effect requires the observation of single muscle execution but also by simple observation of goal directed activation or of more complex muscle synergy pattern; (ii) actions performed by other individuals [3,4]. Moreover, the facilitatory effect depends on mere observation of the Perrett et al. [5] disclosed that goal-directed actions are movement or more on learning instructions; (iii) the also coded by temporal neurons selective for the observa- excitability of right and left motor cortex differs during tion of specific hand-object interactions; these neurons movement observation. remain silent if the movements are the consequence of the animal’s own action [6]. A relationship between movement execution and ob- 2. Methods servation was also demonstrated in humans using transcra- nial magnetic stimulation (TMS) [7]. The authors perform- We studied eight healthy subjects (four male and four ing TMS of left motor cortex in twelve healthy human female; mean age: 3468.9 years); all of them were right- subjects showed a clear enhancement of motor evoked handed according to Edinburgh inventory [9]. The subjects were naive of the experimental purpose and gave their informed consent to undergo the study. During all the *Corresponding author. Tel.: 139-91-655-5108; fax: 139-91-655- 5102. experimental procedure they sat on a comfortable armchair 0022-510X / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0022-510X(00)00271-9