[these are notes from the Neuroscience textbook - not quotes!]

Hypothalamus: what the heck?
hypothalamus is  at the base of the forebrain, bounded by optic chiasm
rostrally and midbrain tegmentum caudally. it forms the floor and ventral
walls of the 3rd ventricle. It is continuous with the posterior pituitary
via the infundibular stalk. It's made of a number of nuclei in three
longitudinal regions called periventricular, medial and lateral zones.
Periventricular zone contains paraventricular and supraoptic nuclei, which
contain neurosecretory neurons with axons extending into the posterior
pituitary, which secrete oxytocin and vasopressin. The suprachiasmatic
nucleus gets direct retinal input and drives circadian rhythms. Medial
zone nuclei, including dorsomedial and ventromedial nuclei, are involved
in feeding, reproduction, and parenting, thermoregulation, and water
balance. medial zone nuclei get input from the limbic system and visceral
sensory nuclei of the brainstem. The lateral zone of the hypothalamus is
mainly a rostral continuation of the midbrain reticular formation. neurons
here control behavioral arousal and attention shifts, especially wrt
reproduction and homeostasis. 

 Limbic System: pp 518 - 524

while the subjective emotional experience might depend on an intact
cerebral cortex, coordinated emotional behavior does not necessarily
depend on cortical processes. Emotions involve phylogenetically older
parts of the nervous system. 

Walter Hess showed that electrical stimulation of discrete sites in
hypothalamus in cats could lead to a rage response and attack behavior.
Stimulation of other sites in the hypothalamus caused defensive posturing
resembling fear. These experiments showed that the control of the
autonomic NS is not entirely separable from the control of other effector
pathways. Stimulation which elicits autonomic responses pretty much always
causes somatic motor responses at the same time.

Hypothalamus projects into reticular formation, and targets include nuclei
controlling waking and sleeping states, cardiovascular function,
respiration, urination, vomiting, and swallowing. These reticular neurons
get hypothalamic input and feed into somatic and autonomic effector
systems in the brainstem and spinal cord. Therefore, hypothalamic activity
can produce widespread autonomic and somatic responses - can override
reflex function, and can involve almost every organ in the body.

Unified emotional behavior, therefore, is acheived through the convergence
in the brainstem reticular formation of hypothalamic and other descending
pathways which control motor neurons. 

James Papez in 1937: investigation of limbic lobe (cingulate gyrus and
hippocampus). He wanted to find out their role in emotional expression.
Ultimately he demonstrated interconnectivity of cortex and hypothalamus
via "Papez' circuit" in which the hypothalamic mammillary bodies project
to the anterior nucleus of the dorsal thalamus, which in turn projects to
the cingulate gyrus, which in turn projects to the hippocampus, which then
projects via the fornix back to the mammillary bodies of the hypothalamus.
Papez believed that this circuit provided the connections necessary for
cortical control of emotional expression. Over time, new elements were
found and the whole mess was called the "limbic system". 

Things added to Papez' circuit that are now considered part of the limbic
system include the amygdala, the prefrontal cortex, association areas, and
possibly the olfactory tract/bulb.

Interrupting Papez' circuit has experimentally caused bizarre behavior in
monkeys.

Amygdala: nuclear mass buried in the white matter of the temporal lobe,
rostral to the hippocampus. Note that the hippocampus really has little to
do with emotion - more involved with learning, short term memory - whereas
the amygdala was hardly mentioned by Papez, and is in fact majorly
involved with emotional control. It occupies the rostral pole of the
temporal lobe. It's made of a mass of grey matter buried in the cerebral
hemisphere, and also some associated cortex on the medial aspect of the
hemisphere's surface. There are three subdivisions to the amygdala. The
basolateral nuclei mainly connect with cerebral cortex, esp sensory
association areas. The corticomedial group of nuclei connects with the
olfactory bulb and olfactory cortex extensively. The central and anterior
group of nuclei is characterized by connections with the brainstem and
hypothalamus, and with viscerosensory areas such as the NS. There are two
main projection pathways in and out of the amygdala - the ventral
amydalofugal system (a diffuse collection of fibers) and the stria
terminalis (a more compact fiber bundle). The amygdala links sensory
cortex with hypothalamic and brainstem effector systems. cortical inputs
provide info about highly processed visual, sensory, and auditory stimuli,
whereas the hypothalamus gets only generally unprocessed sensory input.
The amygdala also gets sensory input directly from some thalamic nuclei
and the olfactory bulb and NS in the brainstem. Projections from the
amygdala to the hypothalamus and brainstem and maybe even cord allow it to
control both autonomic and somatic motor activity.

The amygdala is important in investing sensory experiences with emotional
significance. 

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