Behavioral and Motivational
Mechanisms of the Brain
Functional Brain Systems


Networks of neurons working together
and spanning wide areas of the brain
The two systems are:
– Limbic system
– Reticular formation
Diencephalon



Central core of the forebrain
Thalamus, hypothalamus and epithalamus
Encloses the third ventricle
Reticular Formation

Composed of three broad columns along the length
of the brain stem
– Raphe nuclei
– Medial (large cell) group
– Lateral (small cell) group

Has axonal connections with hypothalamus,
thalamus, cerebellum, and spinal cord
Reticular Formation
Functions of the Reticular Formation
1. Excitatory stimulus to the brain & Consciousness
2. Regulation of muscle relfexes
3. Co-ordination of the autonomic reflexes
(Respiratory and Cardiovascular reflexes)
4. Regulation of pain sensation (Reticulospinal
pathways modulate impuls transmission in the
dorsal horn of the spinal cord)

Brain stem monoaminergic systems play important
roles in the control of these functions
Activating-Driving Systems of the Brain

Continuous transmission of nerve signals from the
lower brain to the cerebrum

Blockage by tumors (e.g. Pineal tumor)

1) Direct stimulation of background level of neuronal
activity in wide areas of the brain

2) Activation of neurohormonal systems that specific
facilitatory or inhibitory neurotransmitters to selected
areas of the brain
Continuous Excitatory Signals
from the Brain Stem

Reticular excitatpry area of the brain

Located in the reticular substance of the pons and
mesencephalon

Also called “bulboreticular facilitatory area”

This system also maintain tone in the antigravity
muscles and controls the levels of spinal reflexes
Continuous Excitatory Signals
from the Brain Stem
Continuous Excitatory Signals
from the Brain Stem

Two types of excitatory signals passing through the
thalamus:

Rapid stimulus (ACh) and Small neurons of the brain
stem (Monoamines)
Excitation of the excitatory area
by peripheral sensory signals

Level of activity of the excitatory area in the brain
stem is determined by the peripheral sensory signals

Stimulation by pain signals

Entrance of 5th cranial nerve to the pons

Transection of the brain stem below or above the
5th cranial nerve
Excitation by the feedback
signals from the cerebral cortex
A reticular inhibitory area
located in the lower brain stem

This inhibitory area is located in the medulla

This area can inhibit reticular facilitatory area
and thus decrease activity in the brain

Inhibitory signals from serotonergic neurons
Neurohormonal Control of Brain Activity
Neurohormonal Control of Brain Activity

Norepineprine system and locus coeruleus: located at the
juncture between the pons and mesencephalon

Dopaminergic system and Substantia nigra: It lies anteriorly in
the superior mesencephalon

Serotonergic system and the raphe nuclei: Located in the
midline of pons and medulla, several thin nuclei called raphe
nuclei

ACh system: Gigantocellular neurons of the reticular formation
(pons and mesencephalon) : tracts go both to the brain and
spinal cord
Neurohormonal Control of Brain Activity
Central Noradrenergic System
Central Serotonergic System
Central Dopaminergic System
Acetylcholinergic System
LDT: Latero Dorsal Tegmental Nucleus
PPT: Pedunculopontine Tegmental Nucleus
Other Neurotransmitters and
Neurohormonal Substances

Enkephalins

Glutamate
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Vasopressin
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Epinephrine

Histamine

Endorphins
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In most places in the brain ACh functions as an
excitatory neurotransmitter
Limbic System
(The Emotional & Motivational Brain)
Emotions
If only it were as simple as the diagrams
below…
Limbic System

Limbic system

Rhinencephalon = smell brain

Hypothalamus, hippocampus, anterior nucleus of thalamus,
septal nuclei, amygdala, paraolfactory area, portions of basal
ganglia
Limbic System

Medial forebrain bundle connects the limbic system
to the brain stem
Hypothalamus

Thalamus and the third ventricle

Mammillary bodies
Relay station for olfactory pathways

Infundibulum – the pituitary gland
Hypothalamus

Output signals from the hypothalamus:

1) Brain stem

2) Diencephalon and Cerebrum

3) Infundibulum – the pituitary gland

Hypothalamus represents less than 1 % of the brain
mass
Papez Circuit (circa 1930)
Hypothalamic Function

Regulates blood pressure, rate and force of
heartbeat, digestive tract motility, rate and depth of
breathing, and many other visceral activities

Perception of pleasure, fear, and rage

Regulation of body temperature
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Regulates feelings of hunger and satiety

Regulates sleep and the sleep cycle

Endocrine functions of the hypothalamus
Vegetative and Endocrine
Functions of the Hypothalamus
Vegetative and Endocrine
Functions of the Hypothalamus

Cardiovascular regulation: Stimulation of posterior
and lateral hypothalamus increases arterial pressure
and HR; preoptic area produces opposite effects

Regulation of body temperature (preoptic area)

Regulation of body water: ADH (vasopressin)

Uterine contractility and milk ejection: Oxytocin

Control of anterior pituitary hormone secretion
Behavioral Functions of the Hypothalamus
and Associated Limbic Structures

Stimulation of lateral hypothalamus

Ventromedial nucleus and surrounding areas

Periventricular nuclei – 3rd ventricle

Sexual drive – anterior and posterior
hypothalamus

Effects of hypothalamic lesions
Reward and Punishment Function of
the Limbic System

Reward centers: Medial forebrain bundle, VMN, LHA

Less potent reward centers reside in the septum and
some basal ganglial areas

Punishment centers: Central gray surrounding the
aqueduct of Sylvius in the mesencephalon,
Periventricular area

Less potent punishment areas are found in the
amygdala and hippocampus
Reward and Punishment Function of
the Limbic System
Reward and Punishment Function of
the Limbic System

Rage and its association with the punishment
centers

Effects of tranquilizers on the reward or punishment
centers

Importance of reward or punishment in learning and
memory
Associative Learning (Fear Response)
Before Training – a
transient orienting
response is induced
to the sound
Training – sound is
paired with the shock
After Training –
placement in the box
induces freezing when
the sound is present.
Memory & Hippocampus

Memory is the storage and retrieval of information

The three principles of memory are:
– Storage – occurs in stages and is continually
changing
– Processing – accomplished by the hippocampus
and surrounding structures
– Memory traces – chemical or structural changes
that encode memory
Hippocampus

Hippocampus and adjacent temporal and parietal
structures are called “hippocampal formation”

This formation has connections with the cerebral
cortex, hypothalamus, septum, amygdala, limbic
cortex and mamillary bodies

Hippocampus is hyperexcitable

Epileptic sezures

Less layers in the hippocampal cortex
Functions of Amygdala

The amygdala is a complex multiple small
nuclei located immediately beneath the
cerebral cortex of medial anterior pole of
each temporal lobe

It has abundant directional connections with
the hypothalamus and other parts of the
limbic system
Functions of Amygdala


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Effects initiated from the amygdala and sent through
the hypothalamus – mostly autonomic functions
Direct stimulation of amygdala results in several types
of involuntary movements
Bilateral ablation of amygdala (Klüwer-Bucy Syndrome)
– Not afraid of anything
– Extreme curiosity about everything
– Forgets rapidly
– Tendency to place everything in mouth & eating objects
– Strong sexual drive
Functions of Limbic Cortex

Cerebral association areas for control of behavior