Modern neuroscience has been underwritten, for much of its history, by an epistemic commitment to the project of cerebral localization – the notion that specific psychic functions can be located within discrete areas of the brain. However, the inauguration in 2013 of the European and American brain mapping projects, both of which emphasize an understanding of individual neuronal connections and brain ‘circuitry,’ might suggest that a major epistemic shift is under way. Yet, as Katja Guenther demonstrates in her elegantly written and deeply researched Localization and Its Discontents: A Genealogy of Psychoanalysis and the Neuro-disciplines, these two epistemic approaches have existed in an uneasy alliance for much of the nineteenth and twentieth centuries. In particular, by tracking the different ways that the concept of the ‘reflex’ was deployed in nineteenth-century German neuropsychiatry, Guenther shows how it could sometimes underpin, and sometimes undermine, the localizationist project. Moreover, by focusing on the institutional and intellectual setting of German neuropsychiatry, Guenther demonstrates how the reflex could be a productive resource for two novel medical fields that are often seen as antithetical: neurology and psychoanalysis.

Guenther's account begins in the shadow of the failed revolutions of 1848 and the reform of Viennese medicine spearheaded by the pathological anatomist Carl von Rokitansky. Rokitanksy's position at the Vienna General Hospital allowed him both to make the pathological laboratory central to medical practice, and to promote the somaticization of psychiatry by giving his institutional support to Theodore Meynert, who would carry out the programme of correlating psychiatric disorder with pathological anatomy. However, this project of functional localization (Zentrenlehre) immediately ran into problems because of the difficulty of clearly locating lesions that corresponded to psychiatric ailments. Instead, Meynert chose to map a more sophisticated form of psychology onto the structures of the brain. By pairing association psychology with the functions of the reflex, Meynert provided an alternative form of localization that could support the broader Zentrenlehre project, and enabled a view of the nervous system as a series of functional units that cooperated socially to produce the complexity of mental life. In addition to paradoxically supporting and undermining the localizationist project, Meynert's ‘association system’ also suggested a clinical application in the form of mental ‘reflex testing’. This clinical procedure was elevated to a high art in the psychiatric clinic (Krankenvorstellungen) of Carl Wernicke, and it is here that Guenther makes one of her most productive contributions to the historiography of the neurosciences. Her sensitive reading of Wernicke's struggles to apply the reflex exam to aphasic patients demonstrates how it could be a rich and productive clinical tool, while simultaneously serving a changing patient population brought about by Bismarckian social reforms. The difficulty Wernicke encountered in correlating aphasic symptoms to simple disturbances in the sensory–motor reflex arc led him to modify the reflex test into a clinical practice that considered the patient within her broader context (a move aided by Wernicke's embrace of Guillaume-Benjamin Duchenne's ‘anatomy of the living’). Wernicke thus emerges as a sophisticated and empathic clinician, rather than in his typical depiction as a therapeutically nihilistic pathologist.

While the reflex could support the project of localization, it could also be used to critique it, and in those critiques Guenther locates the origin of new professional groups that challenged neuropsychiatry. Sigmund Freud employed the reflex to reappraise the strict localization of function in aphasia research, and later the lesion model of hysteria and psychiatric disorder. For Freud, the reflex encompassed the whole of the nervous system (rather than merely an ‘association center’), allowing for unconscious pathological associations that might be the root of hysteric symptoms. These associations could then be uncovered by a modified version of mental reflex testing. This testing could also be employed as a treatment, enlisting the patient in a process of working through pathological associations. Freud's use of reflex theory is, for Guenther, the connective thread that links Freud's pre-analytic thought with his more orthodox psychoanalysis, and her narrative is convincing.

Changing contexts provided an impetus for other therapeutics, and the influx of wounded soldiers following the First World War offered the Breslau neurologist Otfrid Foerster the opportunity to employ the reflex as the basis for several new therapies. Foerster conceived of the nervous system as a social Reflexarbeitsgemeinschaft (reflex community), where sensory–motor reflex arcs could be manipulated, either through surgery or through Übungstherapie (exercise therapy). By providing novel treatments for a speciality long thought to be therapeutically impotent, Foerster provided a rationale for the independent existence of neurology, then under siege from psychiatry in Germany. For both Freud and Foerster, then, the reflex underscored not only intellectual projects, but professional ones as well.

The book concludes with paired chapters that examine how the reflex changed as it was transplanted across the Atlantic. In the seemingly disparate cases of the psychoanalyst Paul Schilder and the neurosurgeon Wilder Penfield, Guenther observes a transformation of the reflex principle. In both instances, the separation of sensory and motor responses reinscribed an independent ‘mind’ that was capable of transparently observing mental phenomena. This ‘cutting of the reflex arc’ had profound consequences for both men: for Schilder, alienation from the New York Psychoanalytic society, and for Penfield, a lifelong search for the physical basis of ‘mind’ at the end of his electrical probe. Penfield's surgical practices reinvigorated brain localization, but at the expense of the reflex. By restoring the reflex to the histories of both the neurosciences and psychoanalysis, Guenther effectively links their disconnected histories, and suggests productive new lines of inquiry for historians of the brain and mind sciences beyond the simple division of psyche and soma. Likewise, for those interested in rethinking the categories of analysis within the history of the human sciences, Localization and Its Discontents will prove to be indispensable reading.