Abstract:

Unconscious fear refers to fear responses that occur without conscious awareness of fear-inducing stimuli. Traditional views suggest that unconscious fear processing primarily relies on the superior colliculus-pulvinar-amygdala pathway, with the amygdala serving as the central hub. However, recent studies on cortical and subcortical structures have significantly expanded this understanding. Research has revealed that beyond the amygdala, structures including the visual cortex, lateral geniculate nucleus (LGN), superior colliculus, and pulvinar can rapidly detect and specifically respond to unconscious fear stimuli, revealing a more complex neural processing network. While numerous studies have explored the neural basis of unconscious fear processing, a systematic integration and analysis of the roles and interactions of various brain regions during early visual processing stages remains lacking. Therefore, this paper focuses on examining the functions and interactions of visual cortical and subcortical regions (LGN, superior colliculus, pulvinar) during unconscious fear processing, aiming to construct a more comprehensive neural network model.

The LGN's function extends far beyond its traditional role as a simple visual relay station. Research indicates that K cells in the LGN project to the visual cortex, forming the neural basis for blindsight. More importantly, the extensive connections between the LGN, thalamic reticular nucleus, and visual cortex enable selective filtering of visual information before conscious processing. Under threat conditions, signal transmission rates from the retina to LGN significantly increase, while the ventral LGN participates in modulating the duration of defensive responses to visual threats. Furthermore, studies on blindsight patients further confirm that the LGN can process threat signals bypassing V1, with functional connections between the LGN and visual cortex providing an alternative pathway for rapid behavioral responses, highlighting the LGN's importance as a key node in unconscious fear processing.

The pulvinar's role in unconscious fear processing is more sophisticated than traditionally understood. While conventional views suggest that the pulvinar merely relays information directly to the amygdala, research has revealed more refined functional divisions, where the inferior pulvinar primarily connects with extrastriate visual areas and superior colliculus, while the medial pulvinar maintains bidirectional connections with the amygdala and frontoparietal regions. Notably, the medial pulvinar's approximately 200ms response latency suggests that it may participate in coordinating cortical assessment of stimulus significance before information reaches the amygdala, rather than simply relaying signals. This complex connectivity pattern establishes the pulvinar as a crucial coordinator in evaluating stimulus biological significance.

The primary visual cortex demonstrates unique capabilities in unconscious threat processing. Through feedforward sweep mechanisms, V1 can rapidly process fear signals independently of feedback from higher visual areas. More significantly, V1 undergoes plasticity through fear learning, forming threat-related memory representations that facilitate rapid and precise processing under unconscious conditions. This plasticity is influenced by multiple regulatory mechanisms, including enhanced amygdala theta oscillations, increased acetylcholine release from the basal forebrain, and enhanced signal transmission between the amygdala and sensory cortex.

Future research should focus on three key directions: First, employing multimodal MEG/EEG-fMRI imaging techniques combined with dynamic causal modeling and Granger causality analysis to investigate temporal characteristics and dynamic interactions between cortical and subcortical structures; Second, developing large-scale neural network computational models to simulate dynamic interactions between key brain regions and predict new neural circuit interaction patterns; Finally, exploring clinical translational applications, particularly developing novel treatment approaches based on unconscious exposure therapy and neurofeedback training, providing new therapeutic strategies for emotional regulation disorders and mental illnesses.

In conclusion, this paper establishes that alongside the amygdala, the LGN, pulvinar, and primary visual cortex constitute critical neural nodes in unconscious fear processing. This not only reflects the diversity of visual processing mechanisms but also exemplifies the distinctive neural patterns that characterize human threat response systems.

Key words: unconscious, fear, neural mechanisms