Physiology Chapter 58: Behavioral and Motivational Mechanisms of the Brain – the Limbic System and
the Hypothalamus
Learning Objectives
1. In what 2 ways does the brain stem activate the cerebral part of the brain?
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Directly stimulating a background level of neuronal activity in wide areas of the brain
Activating neurohormonal systems that release specific facilitory or inhibitory hormone-like
neurotransmitter substances into selected areas of the brain
2. What is the role of the bulboreticular facilitory area?
Also called reticular substance of the pons and mesencephalon
Role: sends signals downward to the spinal cord to maintain tone in the antigravity muscles and
control levels of spinal cord reflexes; sends signals upward to thalamus, which then go to cortex
as well as many subcortical areas
3. What 2 types of signals pass through the thalamus?
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Rapidly transmitted action potentials that excite the cerebrum for a few milliseconds:
originate from large neuronal cell bodies throughout the brainstem and release
acetylcholine
Slowly conducting fibers that synapse in the intralaminar nuclei of the thalamus and
reticular nuclei over the surface of the thalamus: originate from large numbers of small
neurons spread throughout the brain stem reticular excitatory area; have an excitatory
effect that can build progressively for many seconds, suggesting signals are important for
controlling longer-term background excitability level of the brain
4. What determines excitation of the excitatory area?
Excitability – determined by number and type of sensory signals that enter the brain from the
periphery
5. What is the result of transection above/below the 5th cerebral nerves?
Cutting above fifth cerebral nerves (the highest nerves entering the brain that transmit
significant somatosensory signals: activity in the brain excitatory area diminishes abruptly and
the brain proceeds instantly to a state of greatly reduced activity, approaching permanent state
of coma.
Cutting below 5th cerebral nerves: this area leaves much input of sensory signals from the facial
and oral regions; coma is averted
6. Describe positive feedback signals returning to the cerebral cortex
Signals are sent from the cortex to the brain stem excitatory area, which sends more excitatory
signals to the cortex. This positive feedback mechanism maintains the level of excitation of the
cerebral cortex, or enhances it. It allows the beginning activity in the cortex to support more
activity, and leads to an “awake mind”
7. What is the origin of inhibitory signals to the cerebral cortex?
Reticular inhibitory area located medially and ventrally in the medulla. This area inhibits the
reticular facilitory area of the upper brain stem and works by exciting serotonergic neurons.
8. What is the benefit of neurohormonal control?
Neurohormones persist for minutes or hours and thereby provide long periods of control, rather
than just instantaneous activation or inhibition.
9. What 4 neurotransmitters are used and how/where do they work?
Norepinephrine: excitatory; works in virtually every area of the brain
Dopamine: excitatory and inhibitory; works mainly in the basal ganglia
Serotonin: inhibitory; works mainly in midline structures
Acetylcholine: excitatory; gigantocellular neurons of the reticular excitatory area
10. What are the neurohormonal systems in the human brain?
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Locus ceruleus and the norepinephrine system: locus ceruleus located posteriorly at the
juncture between pons and mesencephalon. They secrete norepinephrine, which excites
the brain; has important role in dreaming, REM sleep
Substantia nigra and dopamine system: neurons send endings to caudate nucleus and
putamen (striatum), where they secrete dopamine. Dopamine is inhibitory in the basal
ganglia
Raphe nuclei and serotonin system: raphe nuclei are in the midline of the pons and medulli
and they secrete serotonin into the diencephalon and a few fibers of the cerebral cortex.
This can suppress pain, play an inhibitory role to cause sleep
Gigantocellular neurons of the reticular excitatory area and acetylcholine system: fibers
from gian cells divide into two branches going up to higher levels and down to reticulospinal
tracts. They secrete acetylcholine, which is excitatory and leads to an acutely awake and
excited nervous system.
11. What other neurotransmitters and neurohormones are secreted?
Enkephalins, GABA, glutamate, vasopressing, ACTH, epinephrine, histamine, endorphins,
angiotensin II, neurotensin
12. What is the limbic system and its function?
Limbic system: entire neuronal circuitry that controls emotional behavior and motivational
desires
- Major part of limbic system is hypothalamus with related structures: these control many
internal conditions like body temp, osmolality of fluids, drives to eat and drink and control
body weight (vegetative functions), and these are closely related to behavior
13. Use figure 58-4 to describe the anatomy of the limbic system
Located in the center of the limbic system is the hypothalamus. Surrounding this is are the
subcortical structures: septum, paraolfactory area, anterior nucleus of the thalamus, portions of
the basal ganglia, hippocampus, and amygdala.
Surrounding these subcortical structures is the limbic cortex: a ring beginning in the
orbitofrontal area, extending to subcallosal gyrus, over the top of the corpus callosum in the
cingulate gyrus, passing behind the corpus callosum and down o the ventromedial surface of
temporal lobe to the parahippocampal gyrus and uncus.
On the medial and ventral surface of the cerebral hemisphere is a ring of paleocortex that
surrounds a group of deep structures associated with behavior and emotion. This functions as
2-way communication between the neocortex and lower limbic structures.
14. Where does the hypothalamus send its output signals? Why is this important?
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Backward and downward to the brain stem – reticular areas of mesencephalon, pons, and
medulla
Upward toward many higher areas of the diencephalon and cerebrum – anterior thalamus
and limbic portions of the cerebral cortex
Into hypothalamic infundibulum to control secretory functions of anterior/posterior
pituitary glands
Hypothalamus controls vegetative and endocrine functions with these output signals.
15. Which hypothalamic nuclei are stimulated by excitation of the posterior and anterior parts?
16. Briefly describe the vegetative functions carried out by the hypothalamus
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Cardiovascular regulation:
o Stimulation of posterior and lateral hypothalamus increases arterial pressure and
heart rate
o Stimulation in the preoptic area causes decrease in heart rate and arterial pressure
Regulation of Body Temperature:
o Anterior portion of hypothalamus (preoptic area)
o Increase in temperature in this area increases the activity of temperature-sensitive
neurons, while a decrease in temperature decreases their activity
Regulation of body water:
o Stimulation of thirst center (lateral hypothalamus)
o Stimulation of supraoptic nuclei to cause release of ADH (vasopressin)
Regulation of Uterine Contractility and Milk Ejection
o Stimulation of paraventricular nuclei causes secretion of oxytocin
o Oxytocin causes increase contractility of uterus and contraction of myoepithelial
cells surrounding alveoli
Gastrointestinal and Feeding Reglation
o Stimulation of lateral hypothalamic area causes extreme hunger, voracious appetite
o The ventromedial nuclei contains the satiety center
o Mammilary bodies control patterns of feeding reflexes: licking lips, swallowing, etc.
17. Describe the behavioral effects of stimulation at different loci of the hypothalamus
Lateral Hypothalamus: thirst, eating, general level of activity
Ventromedial Nucleus: opposite lateral hypothalamus; satiety, decreased eating, tranquility
Thin Zone Periventricular Nuclei: fear, punishment reactions
Sexual Drive: several areas; most anterior and most posterior portions
18. Describe the behavioral effects caused by the hypothalamic lesions
Lateral Hypothalamus: decreased drinking and eating, lethal starvation, extreme passivity
Ventromedial: effects opposite to lateral hypothalamus; excessive drinking and eating,
hyperactivity
Lesions in other regions of the limbic system, especially amygdala, septal area, and areas in the
mesencephalon, often cause effects similar to those elicited from the hypothalamus
19. What is the reward, punishment function? Where are the centers for each?
These are affective qualities that determine whether sensations are pleasant or unpleasant.
Reward: along the course of the medial forebrain buncle, lateral and ventromedial nuclei of the
hypothalamus (secondary areas in septum, amygdala)
Punishment: central gray area surrounding aqueduct of Sylvius in the mesencephalon and
extending upward into the periventricular ones of the hypothalamus and thalamus (secondary
in amygdala and hippocampus)
20. What is the rage pattern? Cause?
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Defensive posture
Extension of claws
Lifting tail
Hiss
Spit
Growl
Piloerection, wide-open eyes, dilated pupils
Caused by strong stimulation of the punishment centers of the brain especially in the
periventricular zone of the hypothalamus
21. How do tranquilizers work?
They inhibit both the reward and punishment centers, thereby decreasing the affective
reactivity of the animal. They function in psychotic states by suppressing many important
behavioral areas of the hypothalamus and its associated regions.
22. What role do reward-punishment play in learning/memory?
If a sensory experience does not elicit a sense of reward or punishment, it is hardly
remembered. Even still, repetition without reward/punishment leads to habituation to the
specific sensory stimulus.
If however, the stimulus does cause reward or punishment, the cerebral cortical response
becomes progressively more and more instense during repeated stimulation, and the response
is said to be reinforced.
23. What is the function of the hippocampus?
The hippocampus is an additional channel through which incoming sensory signals can initiate
behavioral reactions for different purposes. Stimulation of different areas of the hippocampus
can cause almost any of the different behavioral patterns: pleasure, rage, passivity, excess sex
drive.
24. What is the result of hyperexcitability of the hippocampus?
Hippocampus is easily hyperexcitable. The result is focal epileptic seizure during which, the
person experiences various psychomotor effects (olfactory, auditory, tactile, and other
hallucinations) even though the person has not lost consciousness and knows these
hallucinations to be unreal.
- The reason for hyperexcitability is that they have a different type of cortex from elsewhere
in the cerebrum, having only 3 nerve cell layers instead of 6
25. What is the effect of bilateral removal of the hippocampus?
Anterograde amnesia: can recall previously learned memories, but have essentially no ability to
learn new information based on verbal symbolism. They often cannot even learn names of new
people. They are capable of short-term memory, but no ability to establish memories lasting
longer than a few minutes.
26. What is the role of the hippocampus in learning?
The hippocampus became a critical decision-making neuronal mechanism, determining the
importance of incoming sensory signals. If the hippocampus signals that an input is important,
the information is likely to be committed to memory.
The hippocampus provides the drive that causes translation of short-term memory into longterm memory. The hippocampus transmits some signal or signals that make the mind rehears
over and over the new information until permanent storage takes place. Without the
hippocampi, consolidation of long-term memories of the verbal or symbolic thinking type is poor
or does not take place.
27. What is the amygdala and what does it do?
Amygdala – complex of multiple small nuclei located immediately beneath the cerebral cortex of
the medial anterior pole of each temporal lobe. It has abundant bidirectional connectiosn with
the hypothalamus as well as other areas of the limbic system.
Function – major divisions of the olfactory tract terminates in the corticomedial nuclei of the
amygdala. Another nuclei, the basolateral nuclei, is more developed .
**Amygdalas are the behavioral awareness areas that operate at a semiconscious level. They
project into the limbic system one’s current status in relation to both surroundings and
thoughts. They make the person’s behavioral response appropriate for each occasion.
28. What are the effects of stimulating the amygdala?
Amygdala signals hypothalamus: increase or decrease arterial pressure, increase or decrease
heart rate, increase or decrease GI motility and secrtion, defecation or micturition, pupillary
dilation, piloerection, secretion pituitary hormones
Amygdala stimulates involuntary movement: tonic movements (raising head or bending body),
circling movements, clonic rhythmical movements, movements of olfaction and eating
Amygdala can stimulate rage,escape, punishment, severe pain, fear, similar to that from the
hypothalamus. Other areas of stimulation here cause reward/pleasure
29. What is the Kluver-Bucy Syndrome? What is its cause?
Caused by destruction of temporal lobes including amygdalas
Symptoms: no fear, extreme curiosity, forgets rapidly, tendency to place everything in mouth,
sex drive so strong it will mate with animals of a different species.
30. What is the limbic cortex? What does ablation of the following zones do to behavior: anterior
temporal cortex, posterior orbital frontal cortex, anterior cingulate gyri and subcallosal gyri
Limbic Cortex – surrounds the subcortical limbic structures: functions as a transitional zone
through which signals are transmitted from the remainder of the brain cortex into the limbic
system; it is a cerebral association area for control of behavior
Destruction of Anterior Temporal Cortex – destroys amygdalas  Kluver-Bucy Syndrome
Destruction of Posterior Orbital Frontal Cortex – insomnia, intense motor restlessness, unable to
sit still and moving about continuously
Destruction of Anterior cingulate gyri and subcallosal gyri – these portions communicate
between prefrontal cerebral cortex and subcortical limbic structures; releases centers of septum
and hypothalamus freom prefrontal inhibitory influence. Animal can become vicious and more
subject to fits of rage.