Archives Italiennes de Biologie, 149 (Suppl.): 18-28, 2011. Carlo Matteucci, Giuseppe Moruzzi and stimulation of the senses: a visual appreciation N.J. WADE School of Psychology, University of Dundee, UK A bstract The senses were stimulated electrically before speculations of the involvement of electricity in nerve transmis- sion received experimental support; it provided a novel means of defining the functions of the senses. Electrical stimulation was used by Charles Bell and Johannes Müller as a source of evidence for the doctrine of specific nerve energies because it resulted in the same sensations produced by natural or mechanical stimuli. The basis for understanding nerve transmission was provided by Luigi Galvani and Alesssandro Volta and elaborated by Carlo Matteucci and Emil du Bois-Reymond, both of whom maintained an interest in the senses. A century later, Giuseppe Moruzzi demonstrated how incoming sensory signals can be modulated by the reticular system. Key words Matteucci • Moruzzi • Nerve impulses • Reticular system • Senses Introduction of the senses. Indeed, the senses have provided an avenue to understanding the brain and its func- Giuseppe Moruzzi (1910-1986, Fig. 1) was born one tions since antiquity. However, sources of stimu- hundred years ago, and this significant anniversary has lation then available were limited: students could been marked by a conference held in Villa di Corliano, report on their experiences when stimulated natu- San Giuliano Terme (Fig. 1) from 22-26 June, 2010. rally, and they could relate them to their body parts. It also celebrated the distinguished physiologist Carlo Additional inferences could be drawn from disease Matteucci (1811-1868, Fig. 1) and the full title of or injury. Recourse was frequently made to philoso- the meeting was “From Carlo Matteucci to Giuseppe phy, usually linking the senses to the elements – fire, Moruzzi: two centuries of European physiology”. earth, water, and air – which permeated perception. Matteucci lived in the Villa for several years (1850- The situation regarding the senses and the nervous 1854), and he would travel by train to the University of system was radically revised in the nineteenth cen- Pisa to conduct his research and to deliver his lectures. tury, with developments in physics, anatomy, and physiology. Sources of stimulation could be speci- fied and controlled more precisely, and among these Stimulating the senses was electricity. In 1752, Johann Georg Sulzer (1720-1779) described Both Matteucci and Moruzzi derived insights into the taste produced by placing different metals in the operation of the nervous system from studies the mouth. When silver was placed on one side Corresponding Author: Nicholas J. Wade, School of Psychology, University of Dundee, Dundee DD1 4HN, UK - Email: [email protected] STIMULATING SENSES 19 Fig. 1. - Upper, Villa di Corliano with superimposed portraits of Matteucci on the left and Moruzzi on the right. Lower left, Matteucci’s eye; the diagram of the eye is derived from his book, the title page of which is shown in Fig. 3. Lower right, Moruzzi’s ascending reticular system. Moruzzi and Magoun described the reticular system in 1949 and the diagram in which Moruzzi’s portrait is embedded is derived from a figure used by Magoun (© Nicholas Wade). of the tongue and lead on the other, he reported a has been written about Volta’s self-administered sour or alkaline taste which was interpreted as due shocks (see Piccolino, 2003) but less attention has to the mechanical vibrations the metals induced. been directed to Fowler’s similar studies. Volta The effects were pursued more systematically by found that very small currents could be experienced Alessandro Volta (1745-1827; 1793, 1800) and by the tip of the tongue, which was in fact more Richard Fowler (1763-1793), both of whom extend- sensitive than the extant physical devices for mea- ed the senses to which electricity was applied. Much surement. Fowler, on the other hand, explored the 20 N.J. WADE senses in what could be considered as heroic self in the head” (1800, p. 427). The shaking did not last experiments (see Jacyna, 1999). Fowler commenced long and when the current was continued he experi- his studies of the senses after reading Volta’s report enced sound and then noise. Both Fowler and Volta (although neither cited Sulzer’s anecdotal obser- found the sensations so disagreeable and considered vation). Rather than placing different metals on them potentially dangerous that they did not wish to and beneath the tongue, as Sulzer and Volta had repeat them. It is likely that the jerking or shaking of done, he applied electrical discharges and noted the head was a consequence of stimulating the ves- the differences in the sensations produced by the tibular system, although very little was then known two procedures: “Both, indeed, are subacid, but as about its functions (Wade, 2003). unlike to each other, as the taste of vinegar is to that Fowler’s observations were amplified in a let- of diluted vitriolic acid” (Fowler, 1793, p. 82). He ter to him from John Robison (1739-1805; 1793). found that the sensations were strongest when the Electrical stimulation was applied to an open wound tongue was at normal temperature, and that reducing and also to a tooth cavity: “I made a piece of zinc its sensitivity chemically also diminished the sensa- having a sharp point, projecting from its end. I tion. The effects of stimulating the eyes were much applied this point to a hole in a tooth, which has more intense than those of taste and smell: flashes sometimes ached a little, and applied the silver of light appeared at the onset and offset of currents in an extensive surface to the inside of the cheek. applied to the region around the eyes. The flashes When the metals were brought into contact, I felt a were distinguished from the long known effects of very smart and painful twitch in the tooth, perfectly pressing on the eye, as no increase in pressure was resembling a twitch of the tooth ack” (p. 172). In involved. Even more intense sensations were gener- his endeavours to increase the intensity of stimula- ated with zinc and gold than with tin-foil and silver. tion, Robinson came close to making a battery: “I Attempting to stimulate the optic nerve itself “by had a number of pieces of zinc made of the size of insinuating a rod of silver, as far as possible, up my a shilling, and made them up into a rouleau, with as nose, and thus arming this nasal branch, I could, by many shillings. I find that this alternation, in some bringing the silver into contact with a piece of zinc, circumstances, increases considerably the irritation, placed upon my tongue, pass this new influence up and expect, on some such principle, to produce a still the course of the nerve, and thus produce the flash greater increase” (p. 173). in the eye. The experiment answered my most san- Applying electrical discharges (galvanic stimulation) guine expectation. The flash, in this way produced, to the tongue, Johann Wilhelm Ritter (1776-1810) is, I think, if any thing, stronger than when the ball provided experimental support for warmth and cold of the eye itself is armed” (pp. 87-88). He used the as sensory qualities. His first reports regarding warm technique to demonstrate that the pupil constricted and cold were in 1801: “Another contrast in sensa- upon stimulation. tion is that between warm and cold… if one brings In contrast to the many experiments involving stim- into contact a zinc pole on the tongue and silver on ulation of the eyes, that of the ears was not repeated the gums, that on the tongue feels very clearly warm, due to its distinctly unpleasant consequences: “On but it feels cold with silver in the same arrangement” placing different metals in the meatus auditorius (p. 458). Thus, stimulation by the positive pole pro- externus of both my ears, and establishing an insu- duced the sensation of warmth, whereas the negative lated metallic communication between them, I felt, pole resulted in experiencing cold. Slightly earlier or fancied that I felt, a disagreeable jirk of my head. in the same year, Christoph Heinrich Pfaff (1773- The metals used were a silver probe, a roll of tin- 1852; 1801) had described the sensation of coldness foil, and a common brass conductor belonging to an when he applied a current to his finger. Ritter (1805) electrical machine. On withdrawing them from my extended the studies on temperature sensitivity on ears, I experienced a feeling similar to that which the tongue as well as the finger; he found that the one has after emerging from under water” (Fowler, sensation could vary according to the intensity and 1793, p. 85). Volta also reported a jerk to his head duration of the current. His general conclusion was when applying a current between his ears: “At the that: “one must consider the sense of temperature moment the circuit was completed I felt a shaking (for warmth and cold) as essentially different from STIMULATING SENSES 21 the common sense, and as a special sense” (p. 10). The manner in which the nerves themselves worked Galvanic stimulation resulted in a short shock as was hinted at by Luigi Galvani (1737-1798, Fig. well as the particular sensation. In the case of tem- 2) when he made a case for ‘animal electricity’ perature sensitivity, Ritter reported that the shock (Galvani, 1791). He applied a discharge from a remained constant even when the sensation changed Leyden jar to the exposed crural nerve or muscle from warm to cold. Rather than merely speculating of an isolated frog’s leg and it twitched.