Limbic System

limbic system

The limbic system (or Paleomammalian brain) is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction (smell). The term ‘limbic’ comes from the Latin limbus, for ‘border’ or ‘edge.’ Some scientists have suggested that the concept of the limbic system should be abandoned as obsolete, as it is grounded more in transient tradition than in facts.

The limbic system operates by influencing the endocrine system (hormones) and the autonomic nervous system (visceral functions, e.g. breathing, urinating, salivating). It is highly interconnected with the nucleus accumbens, the brain’s pleasure center, which plays a role in sexual arousal and the ‘high’ derived from certain recreational drugs. In a 1954 experiment, rats with metal electrodes implanted into their nucleus accumbens as well as their septal nuclei repeatedly pressed a lever activating this region, and did so in preference to eating and drinking, eventually dying of exhaustion.

The limbic system is also tightly connected to the prefrontal cortex. Some scientists contend that this connection is related to the pleasure obtained from solving problems. To cure severe emotional disorders, this connection was sometimes surgically severed, a procedure of psychosurgery, called a prefrontal lobotomy (this is actually a misnomer). Patients who underwent this procedure often became passive and lacked all motivation.

Paul D. MacLean, as part of his triune brain theory, hypothesized that the limbic system is older than other parts of the brain, and that it developed to manage fight or flight circuitry which is an evolutionary necessity for reptiles as well as humans. However, recent studies of the limbic system of tetrapods have challenged some long-held tenets of forebrain evolution. The common ancestors of reptiles and mammals had a well-developed limbic system in which the basic subdivisions and connections of the amygdalar nuclei were established.

French physician Paul Broca first called this part of the brain ‘le grand lobe limbique’ in 1878, but most of its putative role in emotion was developed only in 1937 when American physician James Papez described his anatomical model of emotion, the Papez circuit. Paul D. MacLean expanded these ideas to include additional structures in a more dispersed ‘limbic system.’

Still, there remains much controversy over the use of the term. When it was first coined, it was posited as the emotional center of the brain, with cognition being the business of the neocortex by contrast. This idea almost immediately ran into trouble when damage to the hippocampus, a primary limbic structure, was shown to result in severe cognitive (memory) deficits. And since its inception, the delineating boundaries of the limbic system have been changed again and again by the community.

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2 Comments to “Limbic System”

  1. Hello! Could you please tell me where you got the graphic for this limbic system illustration? I’d like to use it, but don’t want to get sued for copyright violation!

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