Imaging diagnosis
Case 25
The limbic system mainly composes of hypothalamus (mammillary body), fornix, parahippocampal gyrus (entorhinal cortex), hippocampus and amygdalate, thalamus (dorsal medial thalamic nucleus, mammillo-thalamic tract, anterior thalamic nucleus), septal area (beginning of cingulate gyrus) and cingulate gyrus (1). Of these components, mammillary body, fornix, parahippocampal gyrus, hippocampus and amygdalate, are presented in Figs 1 to 3.
Papez circuit means a rotation tract from hippocampas returning to hippocampas via the route: hippocampas - fornix - mammillary body – anterior thalamic tract – anterior thalamic nucleus – cingulated gyrus – parahippocampal gyrus (entorhinal cortex) – hippocampus (1, 2, 3). Amygdalate situates at the lower anterior end of hippocampas and also connects to parahippocampal gyrus and cingulate gyrus via thalamic dorso-medial nucleus(Yakovelev circuit) (4, 5). Amygdalate functions to create signals to release adrenalin and dopamine (4, 5)
The limbic system is one of the most active brain areas during the process of dreaming (6). The main role of limbic system is memory, emotion and motivation which are relevant each other. Especially, emotion and memory are very closely related (1, 6, 7). As shown in Figs 1 (C, D) and 3 (A, B), it might be reasonable that hippocampas which relates with short-term and long-term memory, places adjacent with amygdalate which relates with emotions of anger, fear and love. The hippocampas exists along with the inferior angle of lateral ventricle (Figs 3 A, B, C).
The parahippocampal gyrus connects from cingulated gyrus and mostly exists at the medial side of hippocampas and along with cistern (Figs 1 B, C, D, Figs 2 A B C). The parahipocampal gyrus is reporter to be an important and active region of the limbic system because it involves memory creation and recall visual scenes (7). Further, this gyrus including entorhinal cortex connects to the association area of the cortex for the storage of the final long-term memory via the cingulate gyrus (1, 3, 7). The damage to this parahippocampal gyrus demonstrates a marked decrease in comprehending collective scenes (3,7). Furthermore, abnormalities of parahyppocampal gyrus may be relevant with schizophrenia, Alzheimer disease and hippocampal sclerosis (3, 7).
The cingulate gyrus is considered to regulate emotions and pain and to be involved in helping orient the body away from negative stimuli by predicting and avoiding the negative consequences and helping to elevate motivation (8). It might be convincing to connect directly amygdalate, parahippocampal gyrus and cingulate gyrus via thalamus of dorsal-medial nucleus to regulate emotion.
【Summary】
It is helpful to get well acquainted with the location of limbic system including hippocampas, parahippocampal gyrus and amygdalate on routine axial and saggittal images of MRI for deepening comprehension of brain itself and brain disease. Especially, an axial image of MRI of Fig 3B is imperative to identify hippocampas, hippocampal gyrus and amygdalate.
【References】
1.Nakano I. The limbic system: An outline and brief history of the concept.Neuropathology. 1998;18:211–214.
2.Papez JW. A proposed mechanism of emotion. Arch Neurol Psychiatry.1937;38:725–743.
3.Mark LP, Daniels DL, Naidich TP, Williams AL. Hippocampal anatomy and pathologic alterations on conventional MR images. AJNR Am J Neuroradiol.1993;14:1237–1240. [PubMed]
4.Sah P, Faber ES, Lopez De Armentia M, Power J. The amygdaloid complex: Anatomy and physiology. Physiol Rev. 2003;83:803–834. [PubMed]
5.Alheid GF. Extended amygdala and basal forebrain. Ann NY Acad Sci.2003;985:185–205. [PubMed]
6.Saper CB, Chou TC, Scammell TE. The sleep switch: Hypothalamic control of sleep and wakefulness. Trends Neurosci. 24:726–731. [PubMed]
7.Mark LP, Daniels DL, Naidich TP, Hendrix LE. Limbic connections. AJNR Am J Neuroradiol. 1995;16:1303–1306. [PubMed]
8.Kalivas PW, Volkow ND. The neural basis of addiction: A pathology of motivation and choice. Am J Psychiatry. 2005;162:1403–1413. [PubMed]
2016.9.27
COPYRIGHT © SEICHOKAI YUJINKAI. ALL RIGHTS RESERVED.