Paper in NeuroImage
- Belinda J. Liddell, Kerri J. Brown, Andrew H. Kemp, Matthew
J. Barton, Pritha Das, Anthony Peduto, Evian Gordon and Leanne
M. Williams (2005). A direct brainstem-amygdala-cortical
alarm system for subliminal signals of fear. NeuroImage,
24: 235- 243
We examined whether consciously undetected fear signals engage
a collateral brainstem pathway to the amygdala and prefrontal
cortex in the intact human brain, using functional neuroimaging.
Blindsight lesion patients can respond to visual fear signals
independently from conscious experience, suggesting that these
signals reach the amygdala via a direct pathway that bypasses
the primary visual cortex. Electrophysiological evidence points
to concomitant involvement of prefrontal regions in automatic
orienting to subliminal signals of fear, which may reflect
innervation arising from brainstem arousal systems. To approximate
blindsight in 22 healthy subjects, facial signals of fear
were presented briefly (16.7 ms) and masked such that conscious
detection was prevented. Results revealed that subliminal
fear signals elicited activity in the brainstem region encompassing
the superior colliculus and locus coeruleus, pulvinar and
amygdala, and in frontotemporal regions associated with orienting.
These findings suggest that crude sensory input from the superior
colliculo-pulvinar visual pathway to the amygdala may allow
for sufficient appraisal of fear signals to innervate the
locus coeruleus. The engagement of the locus coeruleus could
explain the observation of diffuse fronto-temporal cortical
activity, given its role in evoking collateral ascending noradrenergic
efferents to the subcortical amygdala and prefrontal cortex.
This network may represent an evolutionary adaptive neural
alarm system for rapid alerting to sources of threat, without
the need for conscious appraisal.