Among the three prototypical clinical presentations within the spectrum of consciousness, delirium (that is, wakeful impaired consciousness) is undoubtedly the most controversial. Unlike sleep and fainting, which the ancients presumably designated in a similar manner as we currently do, this condition has been less clearly defined and has always prompted more theoretical elaboration. Its changeable nature and ubiquity make the characterisation of delirium less stable, especially considering that it appears in multiple forms and can be present in (and caused by) many other mental or physical, acute or chronic conditions.Footnote ¹

First and foremost, it should be emphasised that delirium is nowadays regarded as a cluster of symptoms rather than a diseaseFootnote ² in its own right. In other words, we should not confuse the features of wakeful impaired consciousness with some specific underlying diseases that often trigger it (currently included within the psychiatric domain). It is in this regard that I will challenge several classicists’ simplistic solution of equating all descriptions of diseases involving cognitive compromise with mental illness. Far from attempting an extrapolation of modern categories into ancient texts, by addressing our current framing of these conditions I aim to make the reader aware of the bias with which we approach the sources. Even assuming the low likelihood of finding equivalences between contemporary and ancient theorisations, it is worth bearing in mind that nowadays mental illness and delirium describe utterly different medical realities. (I shall later discuss how this shift in understanding is not a mere change of names, but enables novel insights into terminological and philosophical issues crucial to ancient medical – and also legalFootnote ³ – thought.)

Current medical understanding and definitions

Our current construction of consciousness as a spectrum has already been mentioned in Chapter 1. It is the intermediate areas of this spectrum, particularly those where patients are awake and hyper- or hypoactive but unaware of or disengaged from their surroundings that can be easily confused with madness. It is, therefore, at these points that definitions need to distinguish these different kinds of affections.

My understanding of delirium/wakeful impaired consciousness follows the DSM 5, where it is defined as an acute and fluctuating syndrome characterised by inattention, disturbed awareness and cognition, and in more serious cases, sleep disturbances and hallucinations.Footnote ⁴ Delirium tends to be episodic, self-limited and changeable.

Mental illness, madness or insanity, on the other hand, are considered as an heterogeneous group of chronic conditions (that is, extended in time), which can present various clinical signs, including extreme moods, hallucinations, delusions, thought disorders and negative symptoms (such as apathy, inexpressiveness and lack of motivation).Footnote ⁵ Only the episodes of ‘acute psychosis’ – which sometimes occur in the course of these longer processes – can be equated with delirium, and hence considered as a specific form of impaired consciousness. Acutely psychotic patients seem out of touch with reality, confused, and any of the above-mentioned symptoms can be present.

It cannot be emphasised enough that delirium is neither equivalent nor specific to psychiatric disorders and can occur in many other conditions. Actually, more often than not it happens in the context of severe systemic diseases (infections, head trauma, intoxication, burns) and several neurological conditions. In other words, an episode of delirium can be a symptom of madness, but it is much more often a manifestation of other conditions, and – more importantly – mental illness cannot be diagnosed only through a single episode of delirium.

Another condition that compromises ‘the mind’ in a related and easily mistakable manner is dementia. Patients suffering from dementia are predominantly elderly, and their main characteristic is a chronic and progressive deterioration of the neurocognitive abilities, which interferes with their activities of daily living. Memory, language, visual-spatial skills, judgement and problem-solving capacities tend to be compromised. Serious cases can present depression, apathy, hallucinations, delusions, agitation, insomnia or sleep disturbances. In other words, dementia can also present specific episodes of impaired consciousness in certain moments during its prolonged course.

It seems quite evident from the above that the common feature shared by all these disorders, which sometimes makes differential diagnosis difficult, is the compromising – in one way or another – of the so-called higher order functions (HOFs). This notion subsumes numerous brain capacities including memory, verbal communication, perception, attention (which together allow judgement, decision-making and planning), as well as the bodily manifestation of the former; namely, behaviours, which are the ways in which human beings conduct themselves under certain stimuli, in determined situations or circumstances.Footnote ⁶

Invariably, delirium, mental illness and dementia affect one or several of these HOFs, hence (to use Aitchinson’s terms) their fuzzy edges, which have caused confusion between them, since antiquity up to the present day. As we shall see below, the Hippocratic doctors also had an intuition of these constructs, but contrary to what is implied in recent scholarship, they mostly commented on the compromise of HOFs in acute, changeable and short-lived situations, which we can easily identify as delirium or wakeful impaired consciousness. The later authors that we will analyse, conversely, did pay attention to more persistent and stereotyped disturbances of these HOFs. Nevertheless, they made important efforts to distinguish those chronic conditions from sudden episodic disorders and strived to recognise both types in order to provide a specific treatment for each of them.

Delirium as evidence of changing ideas about disease

Like several other concepts that we have been discussing, a distinct and universally accepted definition of disease can also be problematic, particularly because it acquires different nuances in different specialties. Nevertheless, any modern textbook that addresses medical conditions is, roughly speaking, divided into (at least) four main sections that shape our current idea of illness: clinical presentation, bodily location, aetiology – often related to abnormal functioning, damaged mechanisms or structures – and treatment. It is precisely from the interaction of these elements that the notion of illness or disease emerges. Our construct of any such distinct nosological entity presupposes a unity underlying all these components. Namely, doctors are always – explicitly or implicitly – searching for a cause that alters a certain physiological mechanism in the body, which triggers determined symptoms and which needs to be reverted through certain therapeutic measures to achieve a cure. On the contrary, when that unity fails to exist (or science has not yet discovered a logical explanation to link symptoms, organs, mechanisms and treatment), practitioners talk of syndromes, which are conceived as mere groups of signs and symptoms but not as diseases in their own right.

In order to illuminate the ancient writers’ understanding of the construct ‘disease’, the analysis will be scrutinising the extent to which they organised such elements into a coherent whole. In other words, by looking at the way in which ancient doctors articulated signs and symptoms with the affected parts of the body, the pathophysiological mechanisms and their therapeutic approaches, we will be able to gauge how the concept of disease changed in the medical discourse.