Neurological Examination, clinical cases and neuropsychological ...

23/07/54
Brain mechanisms
for olfaction
(Smell), the nose
brain or
“Rhinencephalon”
and associated
limbic structures
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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.
The limbic system operates by influencing the endocrine system and the
autonomic nervous system. 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. These responses are heavily
modulated by dopaminergic projections from the limbic system. In 1954, Olds
and Milner found dthat t rats with metal tlelectrodes implanted dinto 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.
The limbic system is the set of brain structures that forms the inner border of the cortex. The cortical
components generally have fewer layers than the classical 6‐layered neocortex, and are usually classified as allocortex
or archicortex.
The limbic system includes many structures in the cerebral pre‐cortex and sub‐cortex of the brain. The term has been
used within psychiatry and neurology, although its exact role and definition have been revised considerably since the
term was introduced.
The following structures are, or have been considered to be, part of the limbic system:
Hippocampus and associated structures:
Hippocampus: Required for the formation of long‐term memories and implicated in maintenance of
cognitive maps for navigation.
Amygdala:Involved in signaling the cortex of motivationally significant stimuli such as those related
to reward and fear in addition to social functions such as mating.
Fornix: carries signals from the hippocampus to the mammillary bodies and septal nuclei.
Mammillary body:Important for the formation of memory;
Septal nuclei: Located anterior to the interventricular septum, the septal nuclei provide critical
interconnections
Limbic lobe
Parahippocampal gyrus: Plays a role in the formation of spatial memory
Cingulate gyrus: Autonomic functions regulating heart rate, blood pressure and cognitive and
attentional processing
Dentate gyrus: thought to contribute to new memories and to regulate happiness.
In addition, these structures are sometimes also considered to be part of the limbic system:
Entorhinal cortex: Important memory and associative components.
Piriform cortex: The function of which relates to the olfactory system.
Fornicate gyrus: Region encompassing the cingulate, hippocampus, and parahippocampal gyrus
Nucleus accumbens: Involved in reward, pleasure, and addiction
Orbitofrontal cortex: Required for decision making.
Clinical Correlates of Limbic System:
Amygdala ,,,,,, Fear, Anxiety, Aggressive, Violence, Rage
Hippocampus… Episodic Memories
Cingulate Gyrus …. Instinctive Behaviours, Parenting,
Social bonding, Moral reasoning,
Delayed alternating tasks
Septal Nucleus … Docility,
Hypothalamus ……ANS, Endocrine, Drive, Motivation
Mammillary Body….. Memory retrieval, recall
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