A direct brainstem-amygdala-cortical 'alarm' system for subliminal signals of fear.
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 fronto-temporal 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.
Liddell
Belinda J
BJ
School of Psychology, University of Sydney, NSW 2006, Australia. belindal@psych.usyd.edu.au
Brown
Kerri J
KJ
Kemp
Andrew H
AH
Barton
Matthew J
MJ
Das
Pritha
P
Peduto
Anthony
A
Gordon
Evian
E
Williams
Leanne M
LM
D000328:Adult; D000679:Amygdala / Q000502:physiology*; D001143:Arousal / Q000502:physiology; D001288:Attention / Q000502:physiology; D001364:Awareness / Q000502:physiology; D001931:Brain Mapping; D001933:Brain Stem / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D004193:Discrimination Learning / Q000502:physiology; D004292:Dominance, Cerebral / Q000502:physiology; D017352:Echo-Planar Imaging; D005239:Fear / Q000502:physiology*; D005260:Female; D005625:Frontal Lobe / Q000502:physiology; D006179:Gyrus Cinguli / Q000502:physiology; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008125:Locus Coeruleus / Q000502:physiology; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D010100:Oxygen / Q000097:blood*; D010470:Perceptual Masking / Q000502:physiology; D017397:Prefrontal Cortex / Q000502:physiology; D020649:Pulvinar / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D017603:Signal Detection, Psychological; D013360:Subliminal Stimulation; D013702:Temporal Lobe / Q000502:physiology
D010100:Oxygen