Brain scans map multiple “low road” fear pathways between the human thalamus and amygdala
Animal studies have described “low road” pathways that rush sensory information from the thalamus to the amygdala. A brain imaging study of 113 people now maps several such routes in humans, with some far more consistent than others.
A study published in NeuroImage has mapped several direct pathways between the human thalamus and amygdala that may enable rapid responses to threats. Researchers from the University of Barcelona studied 113 healthy right-handed volunteers, mapping connections using high-resolution diffusion-weighted MRI and tractography. The most consistent and reliable pathways linked the posterior thalamus to the basolateral amygdala, with one running from the inferior colliculus (an auditory hub) to the amygdala, mirroring an auditory fear pathway in rodents.
Connections between the amygdala and the pulvinar (involved in visual attention) were also consistently detected, particularly in the inferior pulvinar. However, connections with the anterior pulvinar were sparse and inconsistent. The mediodorsal nucleus of the thalamus showed a prominent connection with the basolateral amygdala, though it may primarily carry signals from the amygdala.
Intralaminar thalamic nuclei, located centrally in the thalamus, also showed connections to the basolateral amygdala, though these pathways were more variable between individuals and over time. The study supports the existence of multiple direct thalamus-amygdala pathways, suggesting these could facilitate quick transmission of sensory and emotional signals, supporting flexible defensive responses.
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