Download printable poster. Skip to menu Skip to content Skip to footer. Site search Search. Site search Search Menu. The limbic system. Home The Brain Brain anatomy. Hippocampus The hippocampus, like many other structures in the brain, comes as a pair, one in each hemisphere of the brain.
Image: iStockphoto. The three zones are divided on each side into medial and lateral areas by the fornix. The hypothalamic nuclei include the following [ Table 1 ]. James Papez's delineation of a circuit after injecting rabies virus into a cat's hippocampus and monitoring its progression through the brain, unraveled the basis of cortical control of emotion.
Further elaboration of the circuit has included the prefrontal cortex PFC , amygdala and septum among other areas [ Figure 1 ]. The major input to the hippocampal formation arises from neurons in layers II and III of the entorhinal cortex. In addition, some septal and hypothalamic fibres reach the hippocampal formation via the fornix. A few fibres also arrive from the contralateral hippocampal formation via the hippocampal commissure.
The intrinsic connections of the hippocampus involve fibers from the entorhinal area, dentate gyrus, Ammon's horn and the subiculum. The three primary pathways of this area are called the perforant pathway, mossy fibers and Schaffer collaterals. The existence of a fourth pathway, the alvear path from the entorhinal area to Ammon's horn through the alveus, has been questioned.
Investigators debate whether some perforant fibers reach Ammon's horn. The glutamatergic mossy fibers then extend from the dentate gyrus to CA3 pyramidal layer , although some efferent fibers from CA3 project to the fimbria. CA1 is considered the main output of the hippocampus with fibers extending to the alveus, fimbria and then fornix. A supplementary linkage with the subiculum also is believed to be present [ Figure 2 ].
The efferent fibers from the hippocampal region form three groups: precommissural fornix, postcommissural fornix and nonfornical fibers. The precommissural fibers of the fornix may originate from the cornu ammonis or the subiculum. These fibers travel within the fimbria, crura and body of the fornix. The cornu ammonis fibers terminate exclusively in the lateral septal nucleus, whereas the subicular fibers are distributed to nucleus accumbens, anterior olfactory nucleus, lateral septal nucleus, precommissural hippocampus, medial frontal cortex and gyrus rectus.
The postcommissural fibers mostly terminate in the mamillary body, although some fibers also project to the anterior thalamic nucleus, bed nucleus of the stria terminalis and ventromedial hypothalamic nucleus. The nonfornical fibers project directly from the hippocampus to the entorhinal area as well as to the posterior cingulate and retrosplenial cortices and the amygdala [ Figure 3 ].
The amygdala has two major output pathways:. Ventral route via the ventral amygdalofugal pathway terminates in the septal area, hypothalamus and the medial dorsal thalamic nucleus [ Figure 4 ]. The amygdala has also got connections with the basal ganglia circuit via its projections to the ventral pallidum and ventral striatum, which is relayed back to the cortex via the dorsomedial nucleus of the thalamus [ Figure 5 ]. This circuit is relayed via the basolateral amygdala.
This circuit consists of the orbitofrontal and anterior temporal cortex, amygdala especially the basolateral amygdala and magnocellular division of the dorsomedial nucleus of the thalamus frontothalamic pathway , which relays back to the orbitofrontal cortex. The circuit has been proposed as a substrate for the human ability to infer the intentions of others from their language, gaze and gestures Theory of mind and social cognition [ Figure 6 ].
The functions of the various structures of limbic system are outlined below [ Table 2 ]. The limbic structures are closely related to the olfactory cortex and have a role in the processing of olfactory sensation. Amygdala is involved in the emotional response to smell while another limbic structure—the entorhinal cortex, is concerned with olfactory memories [ Figure 7 ].
Amygdala plays a role in food choice and emotional modulation of food intake. The lateral nucleus of the hypothalamus is the center for control of feeding whereas the ventromedial nucleus functions as the satiety center.
Positron emission tomography PET and functional magnetic resonance imaging fMRI have shown that the limbic system is one of the most active brain areas during the process of dreaming.
The limbic system probably interweaves unconscious primal emotions with our conscious cognitive thoughts and perceptions and thereby ties together emotions and memory during rapid eye movement REM sleep to form the content of dreams.
The suprachiasmatic nucleus of hypothalamus is the circadian rhythm generator controlling the sleep-wake cycle. It also sends axons that terminate within the cholinergic basal forebrain, the pedunculopontinethalamic nucleus PPT and lateral dorsal thalamic nucleus LDT. The lateral hypothalamic area LHA contains orexinergic neurons that promote wakefulness. The orexinergic neurons also increase the firing of the locus coeruleus, dorsal raphe and the TMN and in a way, act as a finger pressing the 'flip-flop' circuit switch into the wakefulness position.
Fear responses are produced by the stimulation of the hypothalamus and amygdala. Amygdalar destruction abolishes fear and its autonomic and endocrine responses. Amygdala is also involved in fear learning, which is blocked when long-term potentiation LTP is disrupted in pathways to the amygdala. Imaging studies have shown that viewing fearful faces activates the left amygdala. Rage responses to minor stimuli are observed after removal of the neocortex. The destruction of the ventromedial hypothalamic nuclei and septal nuclei in animals with intact cerebral cortices may induce rage.
Rage may also be generated by the stimulation of an area extending back through the lateral hypothalamus to the central gray matter of the midbrain. Bilateral destruction of the amygdala results in placidity. However, when the ventromedian nucleus is destroyed after the destruction of the amygdala, the placidity generated is converted to rage. Limbic stimulation causes changes in respiration and blood pressure.
The stimulation of the cingulate gyrus and hypothalamus can elicit autonomic responses. There is however little evidence for localization of autonomic responses in limbic circuitry.
The fear and rage responses mediated by the limbic system cause stimulation of various parts of the hypothalamus, especially the lateral areas and produce diffuse sympathetic discharge. Stress via cortical and limbic connections causes release of corticotropin-releasing hormone CRH from the paraventricular nuclei of the hypothalamus. CRH release mediates endocrine and immune responses [ Figure 8 ]. The medial preoptic area of the hypothalamus is a key structure in the central control of male sexual behavior.
Chemosensory efferents from the main and accessory olfactory systems project to the medial amygdala MeA. MeA sends direct and indirect innervations through the bed nucleus of the stria terminalis to the medial preoptic area MPOA. The parvocellular portion of the CTF called the subparafascicular nucleus SPFp seems to be especially important for stimuli related to ejaculation.
The MPOA sends efferents to the paraventricular nucleus of the hypothalamus PVN , the ventral tegmental area, the nucleus paragigantocellularis and other autonomic and somatomotor areas [ Figure 9 ].
The parvocellular part of the paraventricular nucleus PVN of the hypothalamus contains neurons that send direct oxytocinergic and vasopressinergic projections to the lumbosacral cord. Dopamine can trigger penile erection by acting on oxytocinergic neurons located in the paraventricular nucleus of the hypothalamus.
Activation of oxytocinergic neurons originating in the PVN and projecting to extrahypothalamic brain areas, by dopamine and its agonists—excitatory amino acids N-methyl-D-aspartic acid or oxytocin itself or by electrical stimulation leads to penile erection. The inhibition of these neurons on the other hand, by GABA and its agonists or by opioid peptides and opiate-like drugs, inhibits this sexual response.
The activation of these neurons is secondary to the activation of nitric oxide synthase NOS , which produces nitric oxide. At least some of the glutamatergic inputs to the MPOA are from the medial amygdala MeA and bed nucleus of the stria terminalis BNST , which mediate the female-stimulated increase in dopamine, which in turn, enhances copulatory ability.
Extracellular glutamate in the MPOA increases during copulation, especially during ejaculation and increased glutamate facilitates copulation and genital reflexes. The reward circuitry underlying addictive behavior includes amygdala and nucleus accumbens.
The amygdala plays a central role in cue-induced relapse. Relapse associated with cues, stress and a single dose of a drug of abuse Comment: which one? What kind? The pathway of motivated behavior involves the prefrontal cortex, the ventral tegmental area VTA , the amygdala especially the basolateral amygdala and extended amygdala, the nucleus accumbens core and the ventral pallidum. This pathway is involved in the motivation to take drugs of abuse drug-seeking and the compulsive nature of drug-taking [ Figure 10 ].
Pathway for motivated or goal directed behavior modified from Kalivas and Volkow [ 21 ]. There are also links of amygdala differences in those with Autism, depression, posttraumatic stress disorder, and bipolar disorder. The following structures are not structures of the limbic system, but form complex networks and interact closely with the limbic system, aiding in many functions. The cingulate gyrus is part of the cingulate cortex of the brain and is thought to be an integral part of the limbic system.
This area is believed to be helpful in regulating emotions, behavior, and pain, as well as being responsible for controlling autonomic motor function. Damage to the cingulate gyrus can result in emotions being inappropriate, having a lack of fear, impaired sense of pain, and learning impairments. This region has also shown differences in structure in those with Autism, depression, obsessive compulsive disorder, posttraumatic stress disorder, and bipolar disorder, due to its role in emotional processing Yucel et al.
This region controls most autonomic functions such as hunger, thirst, body temperature, blood pressure, heart rate, and sexual activity. The hypothalamus also serves as an interface between the nervous system and the endocrine system and in the regulation of sexual motivation and behavior. In order to control these many functions, the hypothalamus integrates information from other parts of the brain and is responsive to a variety of stimuli, such as light, odor, stress, and arousal. Differences in the hypothalamus have also been associated with conditions such as depression, bipolar disorder, and schizophrenia.
The basal ganglia are a group of structures, situated at the base of the forebrain and top of the midbrain. Its main functions are to regulate voluntary movements, including eye movements, help with balance as well as posture. There is a limbic region of the basal ganglia which has multiple components nucleus accumbens, ventral tegmental area, and ventral pallidum. These areas have shown to be involved in cognitive and emotional behaviors, and with having a role in rewards and reinforcements.
Because of this, it can be linked with addictive behaviors and the formation of habits. In relation to the limbic system, the basal ganglia may also contribute to depression Stathis et al. Damage to the limbic system is dependant on which region is affected. Damage to the hippocampus could lead to deficits in being able to learn anything new, as well as affecting memory.
Hypothalamus damage can affect the production of certain hormones, including those which can affect mood and emotion.
A potential treatment for limbic impairments is deep brain stimulation DBS. Successful treatment of some cognitive disorders such as anxiety and posttraumatic stress disorder has come from DBS of the amygdala.
Similarly, the use of antidepressant medications has shown links with restoring the underlying physiological differences in the limbic system in major depressive disorder Maletic et al. This could be due to the personal involvement by participants when they make emotional judgments involving themselves.
The participants may have seen deceit as a personal threat, therefore leading to increase amygdala activity as a result. They found that the cingulate cortex, hippocampus, and amygdala had observable differences in structure. Emotions: cerebral hemispheres and prefrontal cortex. Autonomic nervous system ANS and physiologic markers of emotion. Three components of emotion and the universal emotions. Next lesson.
Current timeTotal duration Google Classroom Facebook Twitter. Video transcript So let's talk about the limbic system. What is the limbic system? Well, it's a set of structures in the brain. And many of those structures play an important role in regulating emotion. Now, something that gets kind of confusing when you talk about the limbic system is that experts can't actually agree on what structures make up the entire limbic system. So for our purposes, I'm going to address some of the most important structures and ones that everyone pretty much agrees are part of the limbic system.
Now before I get going into the nitty-gritty so to speak, I want to give you a quick overview of what structures we're going to talk about.
And the way I remember these structures is through this little cartoon here. This is a hippopotamus and he's wearing a hat. Now, why this is this hippopotamus wearing this stylish hat?
Well, this is my way of remembering in the four most important components of the limbic system when it comes to emotion.
So we see a hippopotamus here. I'll write "hippo. I'll write "hat. And the reason I think of this is these are the four main structures of the limbic system when it comes to emotion. And these happen to be the four structures that I'd like to talk about. So let's get to a little more complicated diagram. And what you see here is my best attempt at drawing the limbic system. Now, limbic system structures sit on top of the brain stem. And this is the brain stem. And you can imagine this as the very bottom of your brain.
And here's the spinal cord coming out of it. And the spinal cord goes all the way down your back to about your tailbone. Now, the limbic system are these structures up here, that are drawn in bright colors.
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