Herpes simplex encephalitis is an infection involving the limbic system, and thus the fornix. Below are some anomalies of the fornix: Herpes Simplex Encephalitis Since the fornix is part of the limbic system, it is sometimes implicated in the limbic system’s anomalies. However, the amygdala, basal forebrain, and prefrontal cortex have recently been recognized as additional components that play a more profound role in emotions. This circuit was originally thought to be the anatomical substrate of emotional experience. The Papez circuit is involved in memory and learning, emotion, and social behavior. Finally, the parahippocampal gyrus projects to the entorhinal cortex and the hippocampal formation to complete the circuit.The anterior thalamic nuclei project to the cingulate gyrus, which then projects to the parahippocampal gyrus.The mammillary bodies project to the anterior thalamic nuclei through the mammillothalamic tract.The subiculum projects to the mammillary bodies via the postcommissural fornix through the subiculothalamic tract. The Papez circuit starts in the hippocampal formation (subiculum).It is a closed circuit consisting of the following pathways(8): The fornix is also a critical part of the Papez (medial limbic) circuit. The fornix is largely involved in regulating episodic memories, a type of declarative memory encompassing autobiographical information(7). Functions of the FornixĪs the hippocampus’s primary output tract, the fornix’s primary function is transmitting information from the hippocampus to the mammillary bodies and the anterior nuclei of the thalamus.Įxperts believe that fornix plays a crucial role in some aspects of memory, specifically in recalling long-term memory and details from past events(6). These fibers constitute the dorsal fornix(5). These fibers relay onto the mammillary bodies and the thalamus’ anterior nuclei.Ī small number of fornical fibers pass above the corpus callosum’ splenium to reach the structures above the corpus callosum. Meanwhile, the postcommissural fornix comprises the fibers that pass behind the anterior commissure. These fibers relay onto the medial olfactory area (septal nuclei), the ventral striatum, and the cingulate gyrus (band of cortex). The precommissural fornix consists of the fibers that descend in front of the anterior commissure. The fornix columns divide at the anterior commissure’s level and form the precommissural and postcommissural fornix. Then, the column passes through the hypothalamus to reach the mammillary body. The fornix body extends anteriorly and divides into the right and left halves known as the columns of the fornix.Įach column turns downwards in front of the interventricular foramen of Monro. This body arches over the thalamus and under the septum pellucidum (thin vertical membrane), connecting it to the corpus callosum. The crura continue anteriorly and merge in the midline to form the fornix body. The crura both establish a connection with each other across the midline by the partially crossing fibers known as the hippocampal commissure (David’s lyre)(4). The two posterior pillars (crura) arch anterosuperiorly under the corpus callosum’s splenium, one for each hemisphere. The two posterior pillars (crura) arch anterosuperiorly under the splenium of the corpus callosum, one for each hemisphere(3). The fimbriae’s main bulk continues on each side of the cerebral hemisphere and forms the fornix’s crus (crus cerebri). The alveus’ fibers travel posteromedially and aggregate to form the hippocampus’ fimbria (fringe) of the hippocampus. The fornix starts in the hippocampus as the alveus, a collection of myelinated fibers found medially to the floor of the lateral ventricle’s temporal horn. The fornix’s bundle of white matter fibers are prominent on the cerebral hemispheres’ medial aspects. The fornix is a part of the limbic system associated with various cognitive processes, emotions, memory consolidation, and sexual responses(2). This part of the brain originates from the hippocampus in the mesial (medial) temporal lobe and stretches longitudinally to the diencephalon and basal forebrain to form an arch over the thalamus(1). The fornix is an essential part of the limbic system and represents the hippocampus’ most extensive single pathway, connecting it to different subcortical structures. The fornix, which means “arch” in Latin, is a C-shaped bundle of white matter (nerve fibers) in the brain. This photo gallery presents the anatomy of fornix by means of MRI (T1-weighted sagittal, axial and coronal views).
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