MARCO, MORTON’S NEUROMA AND WHY A CULTURAL ANTHROPOLOGIST ATTENDS A NEUROSCIENCE COURSE

Questo è l’articolo che ho presentato come compito conclusivo del corso online “Understanding the brain” (ovvero un corso di neuroscienze di base) dell’Università di Chicago via Coursera che ho frequentato di recente. Ignoro se possa essere interesse di qualcuno, ma – nel caso – io divulgo sempre (anche solo per tirare su il morale a coloro che sono affetti da tal patologia: fa un male cane, a quanto pare, ma si guarisce!).

The protagonist of the case study I want to consider is my friend Marco, who fifteen years ago suffered from Morton’s neuroma in his right foot in a condition so advanced that it had to be resolved surgically. Today I interviewed him in depth about it to perform this assignment.

Morton’s neuroma (1) consists of the growth of fibrous tissue around the nerve between the third and fourth metatarsals of the foot, just prior to nerve branching between the two affected toes. Normally the diagnosis is made fairly quickly based on the patient’s account of intolerable pain and hence verification by MRI, but in my friend’s case, given his high pain tolerance, three months and many specialists passed before it was reached.

The nerve involved is the medial plantar tibial nerve which derives from the posterior branch of the tibial nerve, a branch of the sciatic nerve which in turn is composed of fibers originating in the sacral plexus or spinal nerves in L4-S3 (2), therefore it belongs to the peripheral nervous system – somatic-motor nervous system. Marco describes an intense pain in the support of the left foot, not well localized beyond that it was in the front part of the foot, which radiated as violent electric shocks to the leg not continuous. Even when there was no pain, Marco perceived a lesser stability not only in the foot but also in the leg, probably the result of the elaboration at the level of the spinal cord, brainstem and cerebellum of the perceptions deriving from the same nerve ending (3).

Hence the pattern that until that moment had governed locomotion in its automatic form was altered, and it was necessary to elaborate a new one in order to return to the possibility of walking according to a gait different from the usual and ‘correct’ one. What happened is that, if basic locomotion is generated by the central pattern generators located in the spinal cord, these found themselves having to manage a new situation according to the new perceptual afferents, and therefore to modify the motor pattern in collaboration with signals and instructions coming from the brainstem, the cerebellum and the basal ganglia.

The latters, in fact, from the sensory information received from the medial plantar tibial nerve, from those received from the vestibular area and finally from the intentionality of voluntary movement elaborated by Marco (including the crooked support of the foot in search of less pain and greater stability) in reaction and search for an alternative solution to the automatic correct one now compromised, have developed a block of movements to continue to allow walking. A block that, with repetition, became a new habit (at the level of the basal ganglia) and also a new automatism (at the level of central pattern generators) for that purpose.

When finally, after three months, Marco obtains a diagnosis, he is told that the only possible solution is surgery (exeresis of the neuroma and of the terminal part of the nerve involved), followed by a short stay and a motor rehabilitation of 6 months. He was operated after which, as he himself says, he had to “relearn how to walk, that is to put my foot straight, to be able to lean on my toes if necessary and so on”.

In this case, it is a matter of re-educating the central and peripheral nervous system to the new post-surgery situation (the definitive one), with the same process with which the body had learned, previously, to allow Marco to walk even in conditions of partial impairment of the foot: starting with the new sensory information received from the medial plantar tibial nerve, the targeted attentions to the quality of movement overseen by the cerebellum, and Marco’s voluntary movement intentionalities processed by the basal nuclei again modified the motor pattern, creating a new habit and a new automatism.

The case-study I have briefly reported is actually quite simple. On the other hand, it exemplifies the reason why I consider the study of neurobiology extremely interesting for those who, like me, come from a background as a cultural anthropologist. As cultural anthropologists, in fact, we always stop at the threshold of the ‘body’, of which we can eventually see superficial or existential changes based on specific cultural motivations. But since we are completely ignorant of its functioning mechanisms (primarily those of the nervous system, which govern its automatic and voluntary existence), we do not see how those cultural choices affect its functioning. Still remaining in the area of movement, questions such as “the repetition of a certain posture or movement, perhaps on the occasion of religious rituals, how does it change the perception of self and of the space outside oneself, and what does it create in the body at the level of automatisms or habits?” seem to me to benefit from an integrated approach of the two fields of research, so that neurobiology seems to me a perfect partner of anthropology, able to give answers to the questions that remain suspended, such as those in a valuable, albeit minor, text of Marcel Mauss of almost one hundred years ago entitled “The techniques of the body” (1936) (4) .

But above all I am thinking of questions that are urgent today, in the ‘global village’ in which we live, such as “if the intersection between our biological being and our cultural being, both of which are declined on the basis of our unique experiences, make us irreducible to each other, on what can we build our interpersonal relationships, our mutual understanding and a peaceful and harmonious coexistence among us as much as possible?”.

So there you have it: I believe that from this course I gained an introduction to our neurobiological being that I felt was a serious lack in my attempt of understanding something more about the human being, and one that I will continue to delve into in order to better ask myself this and other questions, and perhaps try to sketch out answers that, though partial, temporary, and subjective, may perhaps have some use in helping us better knowing ourselves and each others so to, as said, maybe better live together on this planet.

References

(1) Griguolo, Antonio, “Neuroma di Morton“.
(2) https://en.wikipedia.org/wiki/Medial_plantar_nerve, article incorporating text in the public domain from page 963 of the 20th edition of Gray’s Anatomy (1918).
(3) Professor Mason’s units 7 and 8.
(4) A synthesis of the essay can be found here.