Biology & philosophy
January 1, 2015
Brian Key
115 citations
Feeling pain requires specific neural architecture that fish lack. While humans readily attribute subjective experience to animals that respond to noxious stimuli, the neural properties necessary for phenomenal consciousness—the subjective feeling of sensory stimuli—are present in mammals and birds but absent in fish. Fish respond to noxious stimuli reflexively and with limited behaviors, not through conscious awareness. The paper proposes a set of fundamental neural tissue properties required for experiencing affective states and concludes that fish do not feel pain.
Frontiers in Systems Neuroscience
January 1, 2022
Brian Key, Oressia Zalucki, Deborah J Brown
9 citations
Subjective experience—conscious awareness—requires a specific neural architecture, not merely activity in higher cortical regions. The authors propose that any system capable of subjective experience must implement stacked forward models that predict the output of neural processing from inputs, enabling prediction, error detection, and feedback control. They call this the hierarchical forward models algorithm. This framework defines a minimal but not sufficient neural architecture necessary for subjective experience. It implies that animals lacking this architecture cannot have subjective experience, regardless of behavior or brain similarities to humans. The approach shifts focus from which brain regions are active to what computations are performed.
Neuroscience of Consciousness
January 1, 2024
Brian Key, Deborah J Brown
6 citations
Internal feeling states like pain, hunger, and thirst are often assumed to directly cause behaviors essential for survival, but this 'causal assumption' conflicts with the standard neuroscientific view of motor action. The authors argue that denying feelings cause behavior does not necessarily lead to epiphenomenalism, which would contradict evolutionary biology. Instead, they propose the 'sense making sense' hypothesis: the function of subjective experience is not to cause behavior but to explain it, in a restricted sense. This framework integrates neural computations for motor control, feelings, and explanatory processes to account for how feelings contribute to our understanding of why we act.
Neuroscience and Biobehavioral Reviews
October 1, 2025
Brian Key, Deborah J Brown
1 citation
The commonsense idea that feelings such as pain cause behavior is challenged. No known mechanism explains how subjectively experienced pain could directly modulate neural activity or gate ion channels. The real cause of behavior is neural activity, not the feeling of pain itself. This raises whether pain has any causal function or is merely epiphenomenal. Epiphenomenalism struggles to explain why such an attention-consuming feeling would survive evolution. The authors infer from neuroscientific evidence that pain has a novel, non-causal function: it marks neural pathways that cause behavior as salient, serving as a ground but not a cause of decision-making and action. Decisions are caused by threshold detection of accumulated evidence of pain, not by pain per se.
The Behavioral and brain sciences
June 25, 2026
Brian Key
The authors argue that the sensory horizons hypothesis fails to explain consciousness because it assumes visual experience directly influences neural activity, but no known mechanism allows subjective experience to generate action potentials. They contend that a more productive approach is to explore non-causal functions of consciousness.
Frontiers in Behavioral Neuroscience
January 1, 2021
Brian Key, Oressia Zalucki, Deborah J Brown
Subjective experience of sensory stimuli depends on the brain's awareness of its own internal neural processing, which in turn relies on predictions from hierarchically organized forward models of internal sensory processing. This specialized neural architecture is required for conscious awareness; without it, a nervous system cannot subjectively experience stimuli. Using nociception as a model, the authors show that the Drosophila brain lacks the internal neural connectivity needed for hierarchical forward models. They conclude that Drosophila and insects with similar neuroanatomy do not subjectively experience noxious stimuli and therefore cannot feel pain.
Frontiers in Physiology
January 1, 2018
Brian Key, Deborah J Brown
Subjective sensory experience, or what it feels like, arises in the cerebral cortex of humans and mammals. While humans verbally report their experiences, other species' awareness is inferred from behavior. Cephalopods have been considered sentient due to complex behavior, but analyzing avoidance learning and brain lesion studies shows no evidence they feel pain. Anthropometric assumptions become questionable with greater phylogenetic distance. Understanding invertebrate sentience requires defining the neural circuits for subjective awareness, which depends on observer neural networks that introspect sensory processing and create predictive internal models. An algorithm using parallel observer networks generates multiple awareness levels; human cortical regions match its predicted circuitry for pain awareness, but cephalopod brains lack the necessary neural architecture. Thus, no compelling evidence indicates cephalopods feel pain.