If you have ever watched the film ‘Awakenings’ starring Robin Williams as Oliver Sacks and Robert De Niro as the Parkinsonian patient Leonard (see Footnote 1) then you will understand that once Sacks’ patients were awakened with L-DOPA that their lives pretty much continued from where they had stopped following a 98% reduction in brain dopamine decades earlier (Sacks 2012). This reduction eliminated a patient’s consciousness by inducing a perpetual state of slow-wave sleep. Slow-wave sleep co-occurs with a diminution of synaptic and metabolic activity within the neocortex (Tehovnik, Hasanbegović, and Chen 2025).

For consciousness to be sustained by the mammalian brain the neural activity of the neocortex must be maintained at a metabolic rate that is 20-times greater than that of subcortical networks (Herculano-Houzel 2011). This principle is also true of fruit flies. The mushroom body of fruit flies is homologous with the mammalian neocortex, and it is this structure that is maintained at a high metabolic rate by a pair of dopaminergic projections so that the animal can store learned information during wakefulness (Plaçais, Preat et al. 2017; see Footnote 2). Dopamine, however, is not sufficient to administer the processes subsumed by consciousness (e.g., learning, memory consolidation and retrieval, the execution of behavior, and so on); it only exhibits the property of turning consciousness on and off in multicellular animals, as exemplified by Oliver Sacks’ Parkinsonian patients (Plaçais, Preat et al. 2017; Sacks 2012; see Fig. 1).

Figure 1: Illustrated is how dopamine regulates state transitions for memory consolidation in the fly (from figure 7 of Plaçais, Preat et al. 2017). Whether such a cellular mechanism is universal across all multicellular organisms deserves verification.

Footnote 1: Currently, ‘Awakenings’ can be watched on Netflix.

Footnote 2: We thank Dr. Mercedes Bengochea of Bengochea and Hassan (2023) for the recommendation of Plaçais, Preat et al. (2017).