RESUMEN
The laterodorsal tegmentum (LDT) is a brain structure involved in distinct behaviors including arousal, reward, and innate fear. How environmental stimuli and top-down control from high-order sensory and limbic cortical areas converge and coordinate in this region to modulate diverse behavioral outputs remains unclear. Using a modified rabies virus, we applied monosynaptic retrograde tracing to the whole brain to examine the LDT cell type specific upstream nuclei. The LDT received very strong midbrain and hindbrain afferents and moderate cortical and hypothalamic innervation but weak connections to the thalamus. The main projection neurons from cortical areas were restricted to the limbic lobe, including the ventral orbital cortex (VO), prelimbic, and cingulate cortices. Although different cell populations received qualitatively similar inputs, primarily via afferents from the periaqueductal gray area, superior colliculus, and the LDT itself, parvalbumin-positive (PV) GABAergic cells received preferential projections from local LDT neurons. With regard to the different subtypes of GABAergic cells, a considerable number of nuclei, including those of the ventral tegmental area, central amygdaloid nucleus, and VO, made significantly greater inputs to somatostatin-positive cells than to PV cells. Diverse inputs to the LDT on a system-wide level were revealed.
RESUMEN
OBJECTIVE: Symptom provocation paradigms using event-related functional magnetic resonance imaging(fMRI) can be an important tool to visualize neuroanatomic correlates of PTSD symptoms. The purpose of this study is to measure regional changes of brain upon exposure to fear stimulus and elucidate the probable relation between signal changes and fear response in PTSD. METHOD: Event-related fMRI was performed during a task where traffic accident-related photos and checkerboards were presented in 9 women with PTSD and 9 woman normal controls in unpredictable order. MRI data were acquired on a 1.5 T GE vision system with a head volume coil. Stimuli were presented on a mirror mounted on the head coil. A total of 200 functional images were taken during a 10-minute scanning session. TR was 3 seconds and inter-stimulus time was varing 4.5 to 11.5 seconds. Data was analyzed using SPM99. RESULTS: In PTSD group, the fear conditions versus the neutral conditions showed activations in both occipital cortex, both fusiform gyrus, left parietal lobule, both insula, right cerebellar tonsil, right putamen, right claustrum, but deactivations in both prefrontal gyrus(p<0.001). In normal control group, activation were found for the fear conditions as compared with the neutral conditions in left fusiform gyrus, both occipital cortex, left parietal lobule, right frontal lobule(p<0.001). CONCLUSIONS: Emotion provocation paradigm using event-related functional magnetic resonance imaging can be applied to illustrate fear response mechanism in PTSD. The result suggests that insula, limbic lobe, cerebellum may play a role in mediating fear response in PTSD.