Early observations

When considering the history of an illness, it is important to recognize that the views of many ancient physicians and philosophers concerning mental phenomena, although they may appear to correspond to our contemporary understanding of an illness, almost certainly referred to symptoms, signs, and behaviours associated with diseases of very varied and altogether different origin. For example, a large variety of infections, left unchecked, can cause marked fever and delirium, which often mimic symptoms of both mania and depression.

Some of the earliest written descriptions of melancholia were penned in ancient Greece by Hippocrates of Cos (460–377 BC) and members of his school who alluded, for example, to irritability, despondency, and an inability to sleep or eat. Interestingly, these writers argued strongly that mental illnesses, such as mania and melancholia, stemmed from organic causes and reflected brain dysfunction, in opposition to the prevailing view of the time, which explained mental illnesses in magical or supernatural terms. Hippocrates considered the brain to be pivotal to the generation of emotions and rejected the role of divine forces [2]. Unfortunately, these ideas, which seem at first sight to correspond to our own modern-day thinking, were based on wholly inaccurate biological models that survive metaphorically. Plato’s (428–348 BC) theory of ideas incorporated rationalism, which has many parallels with modern thinking. He postulated that non-material abstract forms or ideas possess the highest and most fundamental kind of reality. Plato gave psychological importance to childhood trauma and asserted that the psychological significance that people assign to events is more important than the actual events themselves.

The humoral theory, adopted by physicians from Hippocrates until the 19th century, attributed health and disease to a delicate balance between the four humours: blood, phlegm, yellow bile, and black bile. Mania was thought to occur because of excess yellow bile, whereas an over-secretion of black bile (melaina chole) from the liver was thought to culminate in melancholia. As with modern physicians, ancient thinkers and great philosophers did not always agree: Aristotle (himself a student of Plato and tutor to Alexander the Great) assigned much more importance to the heart than he did to the brain. Nonetheless, when considering causality, he too believed that melancholia was a consequence of excess black bile. It was Aristotle who developed the quite visionary concept that some individuals are somehow predisposed to melancholia. He further linked this concept to temperament and, with this coruscating insight, anticipated much of our current ideas regarding biomarkers, vulnerability, and the role of personality and functioning in relation to the mental illnesses of today [3, 4].

Following on from these early concepts, subsequent observers tentatively linked mania and melancholia, suggesting that both either followed similar trajectories or were in fact the same illness, happening to present in varied forms or at different stages of disease. Aretaeus of Cappadocia, who suggested that mania was the end stage of melancholia, made the first definitive link between the two conditions [5]. A physician in Rome during the second century AD, he viewed “mania as a variety of melancholia” and described it as an alternating pattern of illness in which an individual could oscillate between the two forms. Remarkably, he also alluded to cyclothymia and described how personality could, perhaps, contribute to intermittent presentations of manic symptoms. Aretaeus’ rich descriptions of mania detailed a spectrum that overlapped with psychosis, but he only associated the classical form of mania with melancholia. Prophetically, Aretaeus regarded mania as a disorder of the brain, and thus linked it, both phenomenologically and etiologically, to melancholia, which was also of endogenous origin [6].

Other aspects of the mood disorders, as we know them today, were successively added over time as physicians continued to observe patients with mental illness. Galen of Pergamon (AD 131–201), for example, drew out the recurrent nature of melancholia and established it as a chronic condition. But despite these many early insights, the concepts of mania and depression failed to develop further as medicine, and indeed science as a whole, fell prey to religious and spiritual thinking. During these “dark ages,” divinity dominated and mental signs and symptoms were blamed on any number of evil forces, supernatural events, or black magic. Despite the Renaissance, not until the 19th century did a more informed discussion regarding melancholia and mania resume [7].

Great minds thinking alike

In the middle of the 19th century, two French physicians had the same idea at the same time. Both linked mania to depression and, in essence, created the concept of manic-depressive illness. Jean-Pierre Falret termed his interpretation la folie circulaire (circular disorder), which he used to describe a regular continuous succession of mania and depression [8]. Simultaneously, Jules Baillarger described la folie double forme (double insanity), a single illness in which both mania and depression could be manifested [9]. Wilhem Griesinger echoed this union although, more in tune with Aretaeus’ thinking, he formulated mania as the end stage of a progressively worsening melancholia, and thus viewed the two presentations as manifestations of the same entity occurring at different epochs of the illness. Griesinger regarded the illness as having a chronic course that invariably eventuated in a poor outcome. In contrast, Ludwig Kahlbaum and Ewald Hecker identified much milder forms of “circular disorders,” which also manifest an alternating pattern, but which do not develop a chronic course or culminate in dementia [10, 11]. Again, the descriptions by these early observers are prescient of today’s mood disorder subtypes, such as bipolar II disorder and cyclothymia. However, it is noteworthy that not everyone was in concordance with these ideas: many physicians still regarded mania and melancholia as quite separate illnesses with distinct trajectories.

It was at this juncture that Emil Kraepelin synthesized the observations and insights of his predecessors and contemporaries by creating a model that remains with us today [12]. Kraepelin gave definition to manic-depressive illness by separating it from dementia praecox. As it gradually crystallized and took form as a diagnosis, its boundaries underwent gradual successive expansion until manic-depressive illness eventually consumed all forms of melancholia. Kraepelin’s differentiation of manic-depressive illness from dementia praecox (subsequently known as schizophrenia) was predicated on the former being more likely to: (1) have a family history of manic-depressive illness, (2) run a relatively benign course and have a benign prognosis, and (3) manifest an episodic or cyclical pattern of illness. Kraepelin’s model was widely adopted and remains a principal driver in psychiatric classification today. One reason for its success is its relative simplicity, along with the fact that it arose from empirical observations and therefore resonated strongly with clinicians. Another advantage that perhaps also contributed to its popularity and longevity is that it allowed the inclusion of additional causal factors, both psychological and social. It was, therefore, a relatively holistic model, and one that provided an accessible framework for interrogating mental phenomena [13].

Despite a common ancestry, ideas concerning manic-depressive illness developed along different lines in Europe and the United States [14]. In the latter, psychoanalysis played a significant role, along with social and psychological factors, partly because of Adolf Meyer’s influence and emphasis on bio-psychosocial factors, which he termed “ergasiology” [15], and partly because, at the beginning of the 20th century, treatments that were derived from the disease model were largely ineffective. In contrast, European psychiatry maintained allegiance to the medical model of disease, and concepts of manic-depressive illness grew independently from both psychoanalytical and psychosocial schools of thought.