AMYGDALA AND SUBCORTICAL VISION: RECOGNITION OF THREAT AND FEAR

AMYGDALA AND SUBCORTICAL VISION: RECOGNITION OF THREAT AND FEAR
Kamen G. Usunoff1,2, Oliver Schmitt2, Nikolai E. Lazarov1, Dimitar E. Itzev3, Arndt Rolfs4, and Andreas Wree2
1Department of Anatomy and Histology, Medical University, Sofia, Bulgaria,
2Institute of Anatomy, University of Rostock, Rostock, Germany,
3Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria, and
4Albrecht-Kossel-Institute of Neuroregeneration, Centеr for Mental Health Disease, University of Rostock, Rostock, Germany
The amygdala (Am) is a relatively voluminous gray substance, located in the depth of the ventromedial temporal lobe. The

Am has diverse afferent and efferent connections throughout the neuraxis, and is involved in the modulation of neuroendocrine functions, visceral effector mechanisms, and in complex patterns of behavior: learning and memory, aggression and defense, pain modulation, reproduction, food intake, etc. A recently revealed important function of the Am is that it acts as the brain ‘lighthouse’ which constantly monitors the environment for stimuli which signal a threat to the organism. The data from patients with extensive lesions of the striate cortex indicate that unseen fearful and fear-conditioned faces elicit increased Am responses. Thus, also extrageniculostriate pathways are involved. A multisynaptic pathway from the retina to the Am via the superior colliculus and several thalamic nuclei was recently suggested. We here present data based on retrograde neuronal labeling that
the parabigeminal nucleus emits a substantial bilateral projection to the Am. This small cholinergic nucleus (Ch8 group) in the midbrain tegmentum is a subcortical relay visual center that is reciprocally connected with the superior colliculus. We suggest the existence of a second extrageniculostriate multisynaptic connection to Am: retina – superior colliculus – parabigeminal nucleus – Am. This pathway might be very effective since all tracts listed above are bilateral. The function of the Am by the rapid response to the sources of threat before conscious detection is significantly altered by various neuropsychiatric diseases.
Biomed Rev 2008; 19: 1-16.

Key words: emotion, extrageniculostriate visual pathways, limbic system, parabigeminal nucleus, superior colliculus, tract tracing


Correspondence and reprint requests to Dr Kamen G. Usunoff, Department of Anatomy and Histology, Faculty of Medicine, Medical University-Sofia, 1 Sv Georgi Sofiiski St., BG-1431 Sofia, Bulgaria.
Tel. +359-2-9172 525,
E-mail: uzunoff@medfac.acad.bg

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