• MemoryFreud
• neurology
• dynamic neural networksneurophysiology

‘Even if the terminology is alien, the concept is not’

In the manuscript by Schott (see page 122), Freud is reclaimed for neurology by means of a simple network diagram.1 Specifically, Schott has uncovered Freud's disarmingly simple, yet perceptive description and illustration concerning the basis of what would later be considered presynaptic inhibition. The complexity of the brain, reflected by an estimated 10¹¹ neurons connected by 10¹⁵ synapses, remains difficult to conceptualise. To simplify matters and general principles, wiring diagrams of the brain have evolved and remain in popular usage across the clinical neurosciences, none more so than in the fields of memory, cognition and movement disorders. In contrast, others have developed misgivings about wiring diagrams and their proponents, with the apocryphal quote of distrusting anyone who draws a circuit diagram attributed to the eminent neurophysiologist PA Merton.

In the late 1940s, the psychologist Donald Hebb developed an early hypothesis of learning by proposing a mechanism of synaptic plasticity2 (put simply, cells that fire together, wire together). Hebbian learning remains an early model for the process of long-term potentiation that has been usefully applied to an array of computational models, and invoked to explain the development of memory across various animal models, as well as humans.

However, the thrust of Schott's manuscript is that the work of Hebb was anticipated by the manuscript ‘Project for a Scientific Psychology,’ written by Sigmund Freud in 1895, although not published until 1950 (figure 1).3 In the Freud manuscript, the processes of presynaptic inhibition can be clearly identified, with unimpeded transmission promoting postsynaptic facilitation and neural sensitisation. Such processes were identified as the basis of memory and learning (figure 1).

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Figure 1

Sigmund Freud circa 1890s, when he was developing and writing his ‘Project for a Scientific Psychology’ (Hulton Archive/Getty Images).

These concepts have also found favour in the explanation of more general processes linked to neuroplasticity. While it was clear that the human brain developed as a result of experience, presumed through changes in the strength of neural connections, this plasticity was assumed to cease in adulthood. However, it is becoming increasingly clear that all areas of the brain have the potential to undergo plastic change. Furthermore, activity appears to promote plasticity, while in contrast, trauma, damage and nerve injury negatively impact on such processes throughout the neural access, traversing central and peripheral systems.4

So, what should we make of these further considerations arising from the writings of Freud? Clearly, the historical perspectives are fascinating. Unfortunately, however, Freud developed his theories at a time when there was little in the way of scientific methodology and technology available. As a consequence, there was no possibility of taking these concepts forward, nor rigorously or scientifically testing these theories. The links between neurology and psychiatry are variously argued, although many of the shared principles are becoming more, rather than less, manifest with time. As noted by the Nobel Laureate and neuroscientist, Eric Kandel, in his autobiography, if circumstances and wages had been different, Freud may well have developed further as a neuroanatomist and proponent of the neuron doctrine, rather than becoming the father of psychoanalysis.5