Then (1954), The Doors of Perception
The Default Mode Network: Huxley's Reducing Valve Gets a Name
Huxley proposed that the brain functions primarily as a reducing valve, its main job is to filter out most of what could be perceived, allowing only the 'measly trickle' of information useful for biological survival. He borrowed this from Bergson's inhibitory theory of the brain (Matter and Memory, 1896). The claim was philosophical and speculative in 1954; Huxley had no brain imaging evidence and no neuroscientific vocabulary more specific than 'valve.'
Confirmed by Science
The default mode network (DMN), identified by Raichle et al. (PNAS, 2001) using fMRI, is the brain's primary self-referential processing network, active during mind-wandering, self-reflection, and the narrative construction of 'self.' Under psychedelics, DMN activity is dramatically suppressed (Carhart-Harris et al., PNAS, 2012). The REBUS model (Carhart-Harris & Friston, Pharmacological Reviews, 2019) formalizes the mechanism: psychedelics reduce precision-weighting of top-down predictions (the filter), allowing more bottom-up sensory information into awareness. Huxley's reducing valve is the DMN's filtering function. The 2012 paper was titled 'Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin', it operationalized Huxley's 1954 metaphor.