Electrically interfacing the skin for monitoring personal health condition is the basis of skin‐contact electrophysiology. In the clinical practice the use of stiff and bulky pregelled or dry electrodes, in contrast to the soft body tissues, imposes severe restrictions to user comfort and mobility while limiting clinical applications. Here, in this work dry, unperceivable temporary tattoo electrodes are presented. Customized single or multielectrode arrays are readily fabricated by inkjet printing of conducting polymer onto commercial decal transfer paper, which allows for easy transfer on the user's skin. Conformal adhesion to the skin is provided thanks to their ultralow thickness (<1 µm). Tattoo electrode–skin contact impedance is characterized on short‐ (1 h) and long‐term (48 h) and compared with standard pregelled and dry electrodes. The viability in electrophysiology is validated by surface electromyography and electrocardiography recordings on various locations on limbs and face. A novel concept of tattoo as perforable skin‐contact electrode, through which hairs can grow, is demonstrated, thus permitting to envision very long‐term recordings on areas with high hair density. The proposed materials and patterning strategy make this technology amenable for large‐scale production of low‐cost sensing devices.

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SUMMARY1. The hypothesis that interneurones in the 4th lumbar segment (L4) are interposed between group I and group II afferents and hind-limb motoneurones has been tested. Action potentials of single interneurones were induced by ionophoretically applied homocysteate and recorded in parallel with post-synaptic potentials in motoneurones; the latter were recorded from motor axons in the ventral root of the first sacral segment as population potentials, using the sucrose gap technique.2. The action potentials of twenty-four L4 interneurones were found to be followed by either e.p.s.p.s. or i.p.s.p.s in motoneurones. The latencies of the majority of these p.s.p.s were consistent with monosynaptically evoked excitation or inhibition of motoneurones since they exceeded the latencies of antidromic activation of the interneurones from the S1 motor nuclei by only a fraction of a millisecond.3. The dominant input to both the excitatory and the inhibitory interneurones was from group II muscle afferents, in particular from the quadriceps nerve. The latencies of excitation of the interneurones by these afferents indicated a monosynaptic coupling between them. The same interneurones were co-excited by group I and cutaneous afferents and by descending fibres.4. We conclude that not only excitation but also inhibition of hind-limb motoneurones from group II afferents may be mediated disynaptically and that interneurones in the 4th lumbar segment contribute to both.

There is growing evidence that observation of actions performed by other individuals activates observer's cortical motor areas. This matching of observed actions on the observer's motor repertoire could be at the basis of action recognition. Here we investigated if action observation, in addition to cortical motor areas, involves also low level motor structures mimicking the observed actions as if they were performed by the observer. Spinal cord excitability was tested by eliciting the H-reflex in a finger flexor muscle (flexor digitorum superficialis) in humans looking at goal-directed hand actions presented on a TV screen. We found that, in the absence of any detectable muscle activity, there was in the observers a significant modulation of the monosynaptic reflex size, specifically related to the different phases of the observed movement. The recorded H-reflex rapidly increased in size during hand opening, it was depressed during hand closing and quickly recovered during object lifting. This modulation pattern is, however, opposite to that occurring when the recorded muscles are actually executing the observed action [Lemon et al. (1995) J. Neurosci., 15, 6145-56]. Considering that, when investigated at cortical level the modulation pattern of corticospinal excitability replicates the observed movements [Fadiga et al. (1995) J. Neurophysiol., 73, 2608-2611], this spinal 'inverted mirror' behaviour might be finalised to prevent the overt replica of the seen action.

Rhythmic flexion-extensions of ipsilateral hand and foot are easily performed ("easy" association) when the two segments are moved in phase (isodirectionally), whereas great care and attention are required ("difficult" association) to move them in phase opposition. We searched for features distinguishing the two types of coupling by analyzing, on ten subjects: 1) the frequency limit in each association; and, 2) if coupling is modified by inertial or elastic loading of the hand. 1) Subjects were asked to oscillate hand and foot at various paced frequencies, in the easy or in the difficult association for one minute at least. In the easy coupling, the task was performed up to 2.0-2.5 Hz, the duration being thereafter shortened by muscular fatigue. In the difficult coupling when the frequency was increased above 0.7-1.7 Hz, the performance rapidly shortened, not because of fatigue but because of an inevitable reversal to the in-phase movement. The frequency-duration curve always followed a similar decay, although it covered different frequency ranges in the various subjects. 2) The effect of charging the hand with inertial or elastic loads was studied at the subject's preferred frequency, chosen when the hand was unloaded. Without loading, in the easy association the hand cycle slightly lagged the foot cycle while in the difficult one an almost perfect phase opposition was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)