While Freud’s theories have had an enormous impact on psychiatry—psychoanalysis today still uses similar methods to the ones Freud developed in the beginning of the 20th century—they have long been engulfed in controversy. Freud’s psychoanalytical thinking focused on the understanding of human behaviour by gaining access into the unconscious mind. In a typical session on Freud’s sofa you might talk about your dreams and fantasies, letting your mind wander and speak without controlling your thoughts. Freud would listen to you, absorbing your thoughts and interpreting them, unravelling the unconscious conflicts that caused the symptoms for which you came to this session. Unveiling and subsequently dealing with these unconscious conflicts would cure the original symptoms of your mental instability.

One of the major criticisms of Freud lies in the lack of experimental scrutiny that surrounds his methods of baring the unconscious. Such lack of empirical evidence was, and still is, seen as unscientific. In the 1960s and 70s however, the idea of the presence of the unconscious re-emerged and became of particular interest for neuropsychologists who were trying to gain understanding in seemingly unconscious processes in split-brain patients and in disorders such as Alien Hand Syndrome.

In split-brain patients, all the connecting fibres between the two sides of the brain were surgically cut to alleviate severe symptoms of epilepsy such that there are no direct routes for communication between the two halves of the brain any more. While this undoubtedly helped reduced the severity of symptoms, this procedure also had some other interesting effects. In a series of experiments that went on to gain him a Nobel Prize, Roger Sperry showed that each hemisphere could seemingly have simultaneous systems of volition. For instance, when he showed a split-brain patient a picture on the left side of a computer screen, which will be processed by the right side of the brain, the side that usually does not contain the language areas; the patient would tell him that he/she had not seen anything. However, when he then asked the patient to select an object from several alternatives with their left hand (the one controlled by the right hemisphere), they would choose the object that was presented to them just a second ago even though they could not express why they had picked that exact object.

While complete sections of the corpus callosum tend no longer to be performed, similar bizarre “unconscious” desires also manifest themselves in patients with particular brain damage that affects this region. For instance, in patients with Alien Hand Syndrome one hand does something completely different and independent from the other. Perhaps the most famous example was the brilliant and eponymous Dr. Strangelove, a nuclear war expert and former Nazi, whose uncontrollable hand seemed to still be living under the Third Reich. Another compelling example is that of a woman who was determined to smoke a cigarette, but whenever her one hand had put the cigarette in her mouth, the other would grab it and throw it away.

In fact, as Emeritus Professor of Neuropsychology at Oxford Larry Weiskrantz has pointed out, a curious facet of many clinical syndromes caused by brain damage is that, while these patients may lose particular conscious faculties such as being able to recall past events or identify people by their faces, they still retain “unconscious” abilities to do exactly these things. A patient with prosopagnosia may not consciously be able to recognise faces as a result of damage to the temporal lobe, a region in the lower part of the brain particularly important for memory, but will still able to show changes in arousal when seeing someone familiar.

Today, with the advent of fMRI (functional Magnetic Resonance Imaging), we have the ability to look inside the human brain while someone is ‘thinking’; we can observe the processes that go on inside, even the unconscious ones. With such brain imaging techniques, neuroeconomists have already started to gain insight into unconscious thought processing by showing that when we make economic decisions, for instance buying something on eBay, we tend to depend much less on our conscious, rational deliberation and much more on subconscious gut feeling and emotion. Perhaps Professor John-Dylan Haynes at the Bernstein Center for Computational Neuroscience in Berlin made an even more intriguing discovery: he was able to predict, by looking at someone’s pattern of brain activity with functional neuroimaging, what a person is going to do and when they will do it nearly 10 seconds before he or she actually does. In a recent article published in Brain, Robin Carhart-Harris and Karl Friston argue that with the aid of these brain-imaging techniques, Freudian concepts might now be tested experimentally. Until recently, one of the most common ways to analyse brain imaging data was to directly compare networks of brain activation during a specific task to networks of activation during periods where the brain was assumed to be at rest. However, over the past ten years, research pioneered by Marcus Raichle started looking into what was actually going on in the brain during these periods of rest. Surprisingly, he and his colleagues noticed that the patterns of activity during rest periods were remarkably consistent, which lead him and other researchers to suggest the existence of a “default” network. According to Carhart-Harris and Friston this default network might represent intrinsic internal thought remarkably consistent with the unconscious thought processes in Freud’s later theories. Many of the key principles of Freud’s theory they argue, such as ‘the ego‘ (our conscious self) and ‘the id‘ (our unconscious self), echo our current knowledge of how the brain functions on a global level (ie a different set of areas in the brain is active during conscious processing compared unconscious processing).

Could it be that, after his initial success and subsequent fall from grace, Freud has now come full circle? Appropriately, it turns out that even Freud himself had originally attempted a not dissimilar scientific approach in the Project of Scientific Psychology published in 1895. In his neurophysiological theory he suggested that the transfer of energy between neurons in the brain caused unconscious processes, but in the years to come he decided that neuronal processing as understood at the time seemed much too complex for such an interpretation. Therefore, instead of focusing on energy between neurons, he based a new theory on the analyses of the dreams of his patients. He proposed that the unconscious is a result of highly condensed, symbolic thoughts which he called the primary processes, whilst the secondary processes, the highly rational and logical way of thinking, describe the conscious processes. That neuroscientists are currently, consciously or unconsciously, returning to these ideas would likely have amused Freud.