Limbic System

Rolf Kötter, in Encyclopedia of the Neurological Sciences, 2003

Multiple Definitions of Limbic System

A common view of the limbic system is limited to cortical structures (limbic cortex): The C-shaped topography of the cingulate gyrus and hippocampal region (gyrus fornicatus) is completed by Broca with olfactory tract and bulb, together forming the racket-shaped limbic lobe (Fig. 1). This concept is related to the older entity of the rhinencephalon (olfactory brain), and their proximity was reflected until recently in textbooks dealing with limbic and olfactory systems under a common heading. A modern connectivity-based concept of limbic cortex by Lopes da Silva and coworkers is equally based on the gyrus fornicatus but closes its gap with reciprocal fiber projections linking the subcallosal area with the hippocampal regions (Fig. 2).

Figure 1. Great limbic lobe according to Broca (Rev. Anthropol. 1, 385–498, 1878). G., gyrus; Tr., tractus.

Figure 2. Limbic cortex and area numbers according to Lopes da Silva et al. (1990).

Subcortical structures are added to the gyrus fornicatus in the classic Papez circuit consisting of hippocampus, hypothalamus, anterior thalamic nucleus, cingulate gyrus, and their interconnections. While the Papez circuit was originally proposed to form a mechanism of emotional experience and expression, most neuroscientists currently associate the amygdala with (negative) emotions but exclude the hippocampus as a nonemotional cognitive structure. The conglomerate of Broca's limbic lobe, the Papez circuit, and additional brain structures is synthesized by MacLean to the visceral brain and then renamed the limbic system as the center of neuroendocrine regulation and emotions.

In addition to affecting emotions, lesions of various limbic structures can lead to striking memory impairments. Particularly well investigated is the inability of humans and other primates to acquire new memories after extensive bilateral medial temporal lobe lesions. Other lesions to limbic structures evoke complex disorders of personality, cognition, or consciousness.

Recent attempts to establish the extent of the limbic system by more detailed cytoarchitectonics, histochemistry, connectivity studies, or electrophysiology have provided additional anatomical variety involving parts of neocortex, basal ganglia, and brainstem (specifically insular cortex, nucleus accumbens, and formatio reticularis, respectively). These observations have been conceptualized both in horizontally oriented hierarchical and in vertically oriented parallel processing models of the brain. The former is most clearly expressed in MacLean's triune brain concept of three evolutionarily stacked brain developments, where the limbic system is seen to interface the reptilian brainstem with the mammalian neocortex. Parallel processing of limbic and nonlimbic modalities in cortical as well as subcortical structures is a characteristic of the basal ganglia-thalamo-cortical loops proposed by Alexander and coworkers (Fig. 3). Perhaps the most common feature among limbic system concepts is their tendency to consider closed-loop arrangements as a morphological substrate for assumed reverberatory activity. The similarity of such concepts to ideas from cybernetics and systems theory is obvious.

Figure 3. Limbic basal ganglia-thalamo-cortical circuit according to Alexander et al. (Annu. Rev. Neurosci. 9, 357–382, 1986). Nucl. medialis dorsalis p. mc., nucleus medialis dorsalis thalami pars magnocellularis; 24, area 24 of anterior cingulate gyrus.

Today, the term limbic may relate to a multitude of different and partly contradictory structural and functional conglomerates throughout the entire brain. Even with regard to its core structures, the emphasis shifts between cingulate gyrus, hippocampus, amygdala, hypothalamus, and brainstem. Simultaneously, most properties thought to characterize the limbic system are not unique to this system but also apply to other nonlimbic brain structures. Most strikingly, some disturbances of memory, emotional, or cognitive processes attributed to limbic system disorders are known to occur with isocortical, particularly prefrontal and parietal, lesions. “Preservation of the self and the species” is such a comprehensive concept that no part of the brain is excluded from it.

Restricted and unique definitions of the limbic system arise from adherence to a single experimental method and definitory criterion, such as cytoarchitectonical delineation of archicortex or histochemical detection of limbic system-associated protein. Assuming that remaining expert arguments about precise detection thresholds can be resolved, such investigations lead to enumerations of brain structures with poor justification of “limbic” or “system” terminology. In particular, definitions based on single structural criteria remain functionally meaningless since the hope that new methods would incorporate converging evidence of a unique limbic system have remained elusive.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B0122268709007826

Limbic System

C. Stephani, in Encyclopedia of the Neurological Sciences (Second Edition), 2014

Introduction

Neuroscience abounds in references to the limbic system as well as to limbic structures and limbic functions (lat., limbus=border, edge, or hem). Limbic system concepts can be encountered on all descriptive levels, from molecular to large-scale system approaches, and they are frequently mentioned in experimental studies as well as in clinical case reports. Still, the term remains vaguely defined. It may, however, be used as a term describing a group of functions, hence being integrative rather than distinctive. Terms like mesolimbic, retrolimbic, and paralimbic make use of, and directly refer to, it.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B978012385157401157X

Limbic System

R.L. Isaacson, in International Encyclopedia of the Social & Behavioral Sciences, 2001

4.1 Fiber Tracts

The major tracts of the limbic system include the fornix (hypothalamus–septal area–hippocampus), the stria terminalis (amygdala–hypothalamus), the mammillothalamic tract (mammillary bodies of the hypothalamus to the anterior nuclei of the thalamus), and the cingulum bundle (running through the cingulate cortex from one end to the other). Although this last tract is sometimes thought to be a private association pathway for the limbic lobe, actually it carries fibers of neocortical origin forward and backward through the brain.

Of course, as described above, these nuclei, cortical areas, and tracts represent but a rough approximation of the true complexity of the regions and pathways. All of these limbic categories are far more complex than have been described above. The interested reader is referred to Paxinos (1995) for the anatomic details of the rat brain and to Crosby et al. (1962) for the human.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B008043076703477X

Hormones of the Limbic System

Gert J. ter Horst, in Vitamins & Hormones, 2010

III Anatomy of the Limbic System

The limbic system is composed of a group of tightly interconnected brain areas that includes the cingulate gyrus, the anterior thalamus, the hypothalamus and mammillary bodies, the hippocampus, and the amygdala. It was first described in the first half of the previous century by Paul Broca, who coined the name “limbic system” for a part of the circuitry that is currently known as the limbic system. James Papez and shortly thereafter Paul McLean have extended the basic layout of Broca to what is currently known as the limbic system. After World War II, the introduction of neuronal tract tracing methods have significantly contributed to the understanding of the neuroanatomy of the limbic system and its internal connectivity and interactions with brainstem and spinal areas. First electrolytic lesion-based “Fink-Heimer” anterograde tracing and later various retrograde tract tracing techniques like Horse Radish Peroxidase (HRP), fluorescent Fast Blue tracing, and combinations thereof were used to study the anatomy of the limbic system. Later the use of anterogradely transported tracers like radioactive labeled amino acids and in the 1980s the introduction of antibody-based tracing with selective proteins like Phaseolus vulgaris leuco-agglutinin further increased our knowledge of the limbic neuronal network structure. It was soon recognized that the limbic system is critically involved in metabolic homeostasis, neuroendocrine activity, autonomic functions, and mood and emotion.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/S0083672910820175

Neurobiology of traumatic stress disorders and their impact on physical health

Julian D. Ford, ... Christine A. Courtois, in Posttraumatic Stress Disorder (Second Edition), 2015

The limbic system, often referred to as the “emotional brain,” is an area deep in the middle of the brain that is in many ways a bridge between brain areas that lie in the brainstem (such as the locus coeruleus; see Box 5.3) and the frontal cortex (ventromedial/orbital and dorsolateral prefrontal cortex; see Box 5.5). The limbic system is a collection of distinct but interconnected brain regions that play several important roles in fear, stress reactivity, learning, and memory. Hence, it is not surprising that limbic system areas are intimately involved in PTSD.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B9780128012888000054

Neuroepidemiology

C.K. Barha, ... T. Liu-Ambrose, in Handbook of Clinical Neurology, 2016

Limbic system

The limbic system has a central role in many basic functions required for survival, including memory, reproduction, and nutrition. Importantly, it is involved in the experience and expression of emotion. The limbic system is comprised of several functionally and anatomically interconnected cortical and subcortical structures located in the frontal and temporal lobes as well as several multimodal association areas that integrate different sensory inputs (Fig. 4.6). These structures include the orbital and medial prefrontal cortex, insular cortex, cingulate gyrus, parahippocampal gyrus, ventral portions of the basal ganglia, the mediodorsal nucleus of the thalamus, mammillary bodies of the hypothalamus, the hippocampus, and the amygdala. It has been thought of as the “feeling and reacting brain”, in contrast to the “thinking brain”, the cerebral cortex.

Fig. 4.6. Anatomy of the brain and the limbic system. The brain is divided into the brainstem, cerebellum, and cerebrum. The outer layer of the cerebrum, called the cerebral cortex, is divided into four lobes: frontal, parietal, temporal, and occipital. The limbic system is composed of many interconnected structures, several of which are depicted in the right-hand illustration.

From http://www.wpclipart.com/medical/anatomy/brain/brain_2/brain_anatomy.png.

In terms of memory formation, the entorhinal cortex of the parahippocampal gyrus receives cognitive and sensory information from the association areas of the cortex, which it transmits to the hippocampus for consolidation. Long-term potential of granule and pyramidal cells in the hippocampus is thought to be the cellular mechanism for memory formation. Consolidated information is retrieved by the entorhinal cortex and sent to the association areas for encoding into long-term memory.

The limbic system is involved in addiction (Orsini et al., 2015), as many drugs of abuse act on elements of this system, which can lead to the dysregulation of the emotional processing abilities of the limbic system altering reward and punishment signaling in the brain. The neuropsychiatric disorder schizophrenia is related to altered limbic system functioning. Studies have shown reduced volumes of the frontal lobes, medial temporal lobes, and thalamus related to loss of neuropil and reduced neuronal size in patients suffering from this disorder. Schizophrenia seems to be also related to dopamine, as antipsychotic medications used to treat schizophrenia block dopamine transmission at the D2 receptor. Damage to the limbic system can also lead to the Klüver–Bucy syndrome, a rare neurobehavioral disorder. The syndrome causes individuals to put objects into their mouths, become hypersexual, show a lack of normal fear and emotional responses, and have memory loss (Lilly et al., 1983). Another disorder associated with the limbic system is Korsakoff's syndrome, also known as amnestic confabulatory syndrome. The disorder typically results from thiamine deficiency from chronic alcoholism, and leads to loss of recent memory (Kril and Harper, 2012).

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B9780128029732000045

Hormones of the Limbic System

Ralf P. Meyer, ... Marcel Gehlhaus, in Vitamins & Hormones, 2010

I Introduction

The limbic system represents complex core structures in the phylogenetically old part of the mammalian brain. Based on the initial anatomical and functional definitions and descriptions of Broca in 1878, Papez in 1937, and MacLean (Maclean, 1952), the concept of what the limbic system really signifies has changed again and again by the scientific community. Consisting of a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, hypothalamus, and limbic cortex (Conn and Freeman, 2000), the limbic system nowadays can be regarded as a balancing structure in processing input from and to external and internal environment (McLachlan, 2009). Emotional, autonomic, motor, and cognitive responses are determined considerably through memory and motivation or relayed from or to cortical structures like the frontal cortex. Especially, memory and cognition, sexual behavior, and also stress and fear are processed, weighed, and balanced by the limbic system in subtle manner (McLachlan, 2009; Roozendaal et al., 2009).

Many of these neurophysiologic parameters are regulated by so-called neuroactive steroids of either gonadal or brain origin, like testosterone, estradiol, and glucocorticoids (Hojo et al., 2004; Janowsky et al., 1994; McEwen, 1994). The limbic system is considered as a prominent area of neurosteroid biosynthesis and action (Leranth et al., 2003; Yau et al., 2003). Neuroactive steroids are associated with memory, behavior, mood, neuroprotection, aging, and neurotransmission. In addition, steroid hormones were credited with playing an important role in brain development, function, and plasticity (Melcangi and Panzica, 2006). Their corresponding receptors AR, ERα and β, and glucocorticoid receptor (GR) show high concentrations and considerable overlap of expression in the structures of the limbic system. This predominantly applies to the hippocampus, hypothalamus, and amygdala, and also the thalamic region (Kawata, 1995; McEwen et al., 2001; Meyer et al., 2009).

It becomes evident that disturbances in steroid hormone level or action more or less influence limbic system function. Such a disturbance can either originate from endogenous factors like defects in gonadal or cerebral steroid hormone production or from exogenous delivered compounds derived from environment, nutrition, or medication. Several recent studies demonstrate that especially xenobiotics entering the brain via diffusion or transport over the blood–brain barrier can affect steroid hormone metabolism in brain and alter steroid hormone receptor-mediated downstream signaling (Gehlhaus et al., 2007; Killer et al., 2009; Meyer et al., 2006). The resulting effects on brain physiology are suspected to include clinically relevant endocrine disorders with dramatic impairment of quality of life, for example, bad or depressive mood state, sexual deficits, or detrimental effects on cognition (Herzog and Fowler, 2005).

This chapter summarizes the effects of xenobiotics on steroid hormone action in the limbic system and gives an outlook of the situation at the blood–brain barrier when xenobiotics reach the brain. This so-called drug–hormone cross talk appears to affect brain's network function.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/S0083672910820059

The Limbic System in Human Communication1

John T. Lamendella, in Studies in Neurolinguistics, Volume 3, 1977

Publisher Summary

The limbic system plays an important role in human communication of all types. This chapter focuses on the role of limbic system in social and communicative behavior. The limbic system is responsible for the bulk of nonpropositional human communication. This forebrain network of cortical and subcortical structures has been thought of only in relation to its regulation of emotion and motivation, but in fact its range of functional responsibilities is large and includes major segments of social and communicative behavior. It is known that humans share these structures homologously with other mammals, and for nonhuman primates, the limbic system comprises the level of neural activity that controls species-wide communication interactions. The chapter discusses the evolution of the limbic system in human species, its development in human ontogeny, and several human clinical syndromes that have limbic etiologies. It also provides an overview of the relationship between limbic and linguistic communication. Moreover, limbic information processing is of interest not only as a nonverbal fringe to language but also because it lies at the heart of many theoretical issues currently under discussion in linguistics and psycholinguistics.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B9780127463032500105

Organization of the Nervous System I

Wanda G. Webb PhD, CCC-SLP, in Neurology for the Speech-Language Pathologist (Sixth Edition), 2017

Limbic and Paralimbic Structures

The limbic system or limbic lobe (see Fig. 2-11) was named by Pierre Paul Broca, who thought of it as the fifth lobe of the brain. It is occasionally referred to as Broca’s lobe because of this. The “lobe” is on the medial surfaces of the two hemispheres. An archlike pattern of cortex surrounding the nonconvoluted central portions of the brain can be observed on the medial surfaces of the hemispheres with the brainstem removed. This internal circular arch is called the limbic lobe (or limbic system or formation). The limbic system includes the oldest or most primitive cortex, the rhinencephalon, also called the “smell brain.” The prefix rhino means “nose”; the functions of the old animal brain dealt primarily with the sense of olfaction, or smell. Because smell is a much more crucial sense for animals in their adaptation to the environment than it is to human beings, the old brain is relatively large in animals, and the cerebral hemispheres are less well developed.

The histologic makeup of the rest of the limbic system is phylogenetically old in relation to the cerebral hemispheres (neocortex) but not as old as the olfactory brain tissue. The limbic system structures have many connections among themselves as well as connections to the hypothalamus (see “Diencephalon” later in this chapter) and to neocortical structures. In the evolution of the human brain, the older parts have come under the direction of the newer cortical systems, creating a hierarchy. Autonomic and hormonal responses caused by hypothalamic action are under the direction of the limbic structures, which in turn are under the direction of the higher cortical structures. Through these connections, the limbic area helps shape behavioral reaction to sensory input through analysis, reaction, and remembrance of stimuli, situations, reactions, and results.12 Heimer9 asserts that the anatomic and functional characteristics of some of the structures of this area are distinct enough to be considered apart from the others, and he questions the concept of a limbic system. For example, the amygdala is the key structure in emotional behavior and the hippocampus and related structures are of primary importance when discussing memory (see Chapter 9).

Mesulam11 conceives of the limbic system as being formed by several smaller structures, including the subcallosal gyrus, cingulate gyrus, isthmus, hippocampal gyrus, and uncus. A medial view of the left hemisphere indicates some of these structures (see Fig. 2-11). The cingulate gyrus (gyrus cinguli) arches over the corpus callosum, beginning at the anterior subcallosal area and arching back to the junction with the parahippocampal gyrus. This juncture is called the isthmus. The uncus is the knob or hooklike area of the parahippocampal gyrus. Mesulam includes in the limbic system structures that are cortical-like in archetype. Cortical-like refers to the fact that their formations are part cortical and part subcortical nuclear in architecture. These structures are the amygdala (or amygdaloid body), substantia innominata, and septal area. They are formed by the simplest and most undifferentiated type of cortex in the forebrain.

A second associative area of cortex is composed of the paralimbic areas (see Fig. 2-11). Although some neuroanatomists include these areas as part of the limbic system rather than refer to them as paralimbic,12 Mesulam11 points out that gradual increases in complexity of the cortex can be found in these areas when compared with the previously mentioned limbic system formations. These structures form an uninterrupted girdle around the medial and basal aspects of the cerebral hemispheres. The paralimbic areas include the caudal orbitofrontal cortex, insula, temporal pole, parahippocampal gyrus (proper), and cingulate complex. The caudal orbitofrontal cortex includes Brodmann areas 10, 11, and 4710 (see Fig. 2-5). The cingulate complex includes the tissue of the anterior cingulate and middle cingulate cortex. Studies of these areas have shown different functional connections for these anatomically close areas. Strong connections with limbic and autonomic functional areas have been traced for the anterior cingulate cortex. The middle cingulate cortex connections are primarily with cognitive processing and sensorimotor processing areas.18

The parahippocampal gyrus completes the C shape of the “limbic lobe.” Most of the rostral part of the parahippocampal gyrus is occupied by an area known as the entorhinal area, which can be identified by its irregular surface (similar to an orange peel). The entorhinal cortex is closely related to the hippocampus.

If the premise is accepted that cortical functioning is hierarchical and a vast network of interrelated functional systems have different, but similar, neuroanatomic substrates, then the study of the functional systems (such as language, memory, emotion) and their disorders must be tempered with the knowledge that brain function is highly complex, with interdependent systems throughout, and only partially understood. While functional subunits of brain operations are studied, attempts to analyze and synthesize the integration of the neural systems that control human behavior continue at a rapid pace.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B9780323100274000026

Anterior cingulate cortex, pain perception, and pathological neuronal plasticity during chronic pain

Fernando Kasanetz, ... Thomas Nevian, in The Neurobiology, Physiology, and Psychology of Pain, 2022

Mini-dictionary of terms

Limbic system: Set of brain regions recognized to participate in emotion, memories, and arousal. Its activation can modulate reinforcing behaviors and lead to autonomic or endocrine responses.

Neuronal ensembles: A population of neurons, closely grouped or diffusely distributed, capable of firing together to participate in a particular neural computation.

Neuronal plasticity: Activity-dependent functional and/or morphological modifications of neuronal properties and synaptic connections.

Optogenetics: Technique that combines genetic engineering to express light-sensitive ion channels in cells with the use of light stimuli to manipulate the activity of neurons.

Calcium imaging: Microscopy technique using fluorescent molecules that change their fluorescence properties when binding Ca2 + ions. In individual neurons, changes in the level of fluorescence correlate with firing activity.

Read full chapter
URL: https://www.sciencedirect.com/science/article/pii/B978012820589100018X