Here’s a fascinating article via a Prague-based (Charles University) neuroscientist and psychologist correspondent of mine Petr Bob. The article of course presupposes familiarity with Kafka’s writings and diaries. Here’s an excerpt from the article – the full article is freely available:

What relevance do the neurobiological studies have to Kafka’s writings?

Kafka deliberately scheduled his writing during the night in a sleep-deprived state. It is also known that he drew from hypnagogic imagery in his stories [40]. In his Diaries, Kafka describes his nocturnal writing as conducted “entirely in darkness, deep in his workshop” [26], p. 518; see also [14]. As Kafka reports, writing without sleep enables access to unusual thoughts and associations which otherwise would be inaccessible: “How easily everything can be said as if a great fire had been prepared for all these things in which the strangest thoughts emerge and again disappear” [26], pp. 293-4, my translation). With regard to this transformed state of consciousness, he writes, “all I possess are certain powers which, at a depth almost inaccessible at normal conditions, shape themselves into literature…” [41], p. 270.” Similarly, Kafka writes in his Diaries, “Again it was the power of my dreams, shining forth into wakefulness even before I fall asleep, which did not let me sleep… I feel shaken to the core of my being and can get out of myself whatever I desire. It is a matter of … mysterious powers…” (cited by Corngold, [42], p. 23). Sleep deprivation may serve as a non-drug “psychotomimetic” model (i.e., producing a psychotic like state in healthy individuals) with attendant changes in dopamine in the striatum and NMDA and AMPA ionotropic glutamate receptor function in pre-frontal cortex [43]. Indirectly, this suggests a possible relationship between intrusive hypnagogic imagery (which is increased with sleep deprivation) and the experiences of beginning psychosis [44], and below.

Kafka’s “great fire” suggests a creative process which provides its own illumination even in darkness. It also suggests a state of cortical excitability (and resulting hypnagogic hallucinations) following Kafka’s withdrawal from sensory/social stimuli coupled with sleep deprivation. Kafka longs for “complete stillness” (as Gregor in The Metamorphosis) eager to separate himself, while writing, from his argumentative family with whom he lived for a good part of his life.xix The Hunger Artist “withdraws deep within himself paying no attention to anyone or anything” [10], p. 268. Kafka is avoidant of unnecessary stimulation, which may also be prompted by his severe headaches [15], and sleeplessness [12], p. 231. However, the withdrawal from photic and social stimulation is also prerequisite for the self-induction of hypnagogic-like trances.

Kafka marveled at the automaticity of his own writing. In a letter to his future betrothed, Felice Bauer – whom he persistently tries to discourage, as evidenced by this letter, from wanting to marry him – Kafka writes: “I have often thought that the best mode of life for me would be to sit in the innermost room of a spacious locked cellar with my writing things and a lamp. Food would be brought and always put down … outside the cellar’s outermost door. … And how I would write! From the depths I would drag it up! Without effort! For extreme concentration knows no effort” [41], p. 156). Here we find solitude, the reduction of sensory stimulation in the cell’s darkness, and the automaticity (effortlessness) of the writing process. According to Kafka’s own reports, he experienced writing (at least in its initial phases) as automatic, effortless and informed by hypnagogic imagery.xxx When writing is effortless, it is the product of a trance-state called “flow” shown to facilitate optimal mental functioning (Csikszentmihalyi, [45]). Kafka writes, “All I possess are certain powers which, at a depth inaccessible under normal conditions, shape themselves into literature…” [41], p. 270). In a letter to Max Brod, Kafka [46] writes that it is “not alertness but self-oblivion [that] is the precondition of writing” (p. 385).

While Kafka was writing, the psychoanalyst, Herbert Silberer, in 1909, conducted introspective experiments [47]. Sleepy one afternoon, he struggles to think through a philosophical problem. To his astonishment, the dream-images which appear while dosing off represent the concepts he was just considering but now in pictorial-visual form (as if in a rebus puzzle). Such images or hallucinations, which are experienced between waking and sleep, are called hypnagogic (hypnagogic from Gk. hupnos ‘sleep’ + agōgos ‘leading’ (from agein ‘to lead’, thus a leading into sleep). Encouraged by this observation, he conducts introspective experiments observing what happens while attempting to maintain cognitive effort as best he can while falling asleep. He concludes that the hallucination “… puts forth ‘automatically’ … an adequate symbol of what is thought (or felt) at a given instant” p. 196 [47]. Silberer gives the example of falling asleep while thinking through a solution he later admits “forces a problem into a preconceived scheme.” His thinking is followed by the hypnagogic-symbolic image: “I am pressing a Jack-in-the-Box into the box. But every time I take my hand away it bounces out gaily on its spiral spring” p. 204 [47]. He interprets the hypnagogic-image to be “autosymbolic.” Its content refers to the thought process, mental-function or feeling in conscious awareness that just preceded it before falling asleep. It occurs in the “transitional,” “twilight” state between sleep and waking in which hypnagogic/hypnopompic images are spontaneously produced. Critically, the autosymbolic hallucination requires that the subject is unaware at the time that his own mind is producing it or its symbolic meaning. Pertinent to our analysis, the phenomenological psychiatrist, Klaus Conrad drew similar conclusions both from introspective observations of hypnagogic imagery and his clinical observations of paranoid psychosis in early schizophrenia, see [48,49] and below. For discussion of the limited reception of Silberer’s work, see [50].