The Diencephalon
Basic Neuroscience
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James H. Baños, Ph.D.
Overview
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Parts of the diencephalon
Thalamus
Hypothalamus
The Diencephalon
The Diencephalon
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Four major parts:
Epithalamus
 Dorsal Thalamus
 Subthalamus
 Hypothalamus
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The Diencephalon
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Epithalamus
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Pineal gland
A few nearby
structures
Pineal Gland
The Diencephalon
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Pineal Gland
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Unpaired midline structure
Just rostral to superior colliculi
Looks like a pine cone (“pineal”)
Endocrine gland related to seasonal light cycles
Secretes melatonin
Clinical Correlation
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What did Descartes think?
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Clinical Correlation
Clinical Correlation
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Pineal Tumor
Hydrocephalus. Why?
 Eye movement abnormalities. Why?
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The Diencephalon
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Dorsal Thalamus
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Thalamic hemispheres
80% of diencephalon
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The Diencephalon
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Subthalamus
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Zona incerta
Subthalamic nucleus
The Diencephalon
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Hypothalamus
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The Diencephalon
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Hypothalamus
Mammilary Bodies
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Infundibulum
Dorsal Thalamus
Functional Roles
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Thalamus has four basic functional roles:
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Sensory
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Motor
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Motor system outputs from the basal ganglia and cerebellum are
relayed by the thalamus
Emotion/memory
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All sensory information (except olfaction) is relayed to the cortex via
the thalamus
The thalamus is part of the Papez circuit and helps control some
emotional and memory information going to limbic cortex (cingulate
gyrus)
Vegetative
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The thalamus has some intrinsic nuclei associated with alertness
and arousal. Can be associated with disorders of consciousness
Thalamus Trivia!!
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What is the single largest source of input
to the thalamus?
Functional Roles
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Thalamus doesn’t just send information to
the cortex. It receives cortical feedback
This signal helps regulate what is coming to
the cortex
 Cortical input is a feedback inhibition loop,
letting the thalamus know that information has
been received and inhibiting further relaying
of the information
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Anatomic Divisions
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Internal medullary lamina
Thin sheet of myelinated fibers
 Divides the thalamus into four major divisions,
each containing specific nuclei:
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Anterior
 Medial
 Lateral
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Not included in these divisions are
The intralaminar nuclei
 The Reticular nucleus
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Anterior
Medial
Lateral
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See p. 392
Anatomical Divisions
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Anterior Division
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Medial Division
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Anterior nucleus
Dorsomedial Nucleus (DM)
Lateral Division
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Dorsal Tier
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Lateral dorsal (LD)
Lateral Posterior (LP)
Pulvinar
Ventral Tier
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Ventral Anterior (VA)
Ventral Lateral (VL)
Ventral Posterior (VP)
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Ventral posteriolateral (VPL)
Ventral posteriomedial (VPM)
Anatomical Divisions
…But wait…there’s more…
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Medial Geniculate Nucleus (MGN)
Lateral Geniculate Nucleus (LGN)
Intralaminar Nuclei
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Centromedian (CM)
Parafascicular (PF)
Reticular Nucleus
LD
A
A
DM
VL
Pulv
Ret
VA
VL
CM
PF VPL
VPM
MGN
LGN
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Pulv
DM
A
See p. 392
VA
VPL
VL
Ret
Functional Divisions
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Another way to think of this
Relay nuclei (i.e., relay to the cortex)
 Association nuclei
 “Other” nuclei
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Interlaminar
 Reticular
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Functional Divisions
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Functional Divisions
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Relay Nuclei
Relay specific information from a particular
tract or modality
 This is not just sensory information
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Relay nuclei are part of several important
modulatory loops in the CNS
This is not simple “passing on” of the signal
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Relay nuclei engage in some complex condensing
and processing of the incoming raw information
Functional Divisions
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Association nuclei
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Support areas of association cortex
Prefrontal cortex
 Parietal-occipital-temporal cortex
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Association cortex is involved in higher
cognitive function
Other Nuclei
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Intralaminar nuclei
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Inputs are diverse!
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Cortex, basal ganglia, cerebellum, brainstem
reticular formation, spinothalamic tract
Project to
Widespread areas of cortex
 Basal ganglia
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Produce general changes in cortical function
Other Nuclei
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Reticular nucleus
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Sheet-like layer of neurons partially covering the
thalamus
Receives input from widespread cortical areas
Only thalamic nucleus with no projections to the
cortex
Inhibitory projections to specific thalamic nuclei
Regulates the activity of the thalamus in the form of
cortical feedback
Clinical Correlation
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Thalamic Stroke - What’s the number one
symptom you might predict?
Clinical Correlation
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Thalamic Stroke
Loss of consciousness/coma
 Attention/arousal problems
 Widespread disruption of cortical function
 Severe cognitive deficits
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Clinical Correlation
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Anterior nucleus
Part of the Papez Circuit in the limbic system
 Involved in memory
 Unilateral Damage: Encoding deficit
 Bilateral Damage: Severe encoding deficit
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Hypothalamus
Hypothalamus
Caudate
Ventricle
Thalamus
Putamen &
Globus pallidus
Hypothalamus
Amygdala
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Hypothalamus
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Pituitary Stalk
Hypothalamus
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Hypothalamus Coordinates Drive-Related
Behaviors
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What are “Drive-related behaviors?”
Hypothalamus
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Behaviors follow the principal of
homeostasis
“Drive” refers to drive to correct
homeostatic imbalance
Hunger/satiety
 Thirst
 Sexual behavior
 Temperature regulation
 Sleep
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Hypothalamus
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Hypothalamus is also the integrative link
between the external and internal
environment
External Environment
Hypothalamus
Internal Environment
Hypothalamus
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Interaction with external environment
occurs through integration with the cortex
Interaction with the internal environment
occurs through:
“Sampling” of blood and CSF
 Release of hormones (via the pituitary)
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The position of the hypothalamus is not a
coincidence
Anatomic Considerations
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Can be divided into three regions
Each region includes medial and lateral zones
Posterior
Anterior
Tuberal
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Anatomic Considerations
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Three regions X two zones = six areas containing nuclei
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Anatomic Considerations
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See p. 563
Anatomic Considerations
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Inputs
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Widespread!
Cortex
 Limbic system
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Helps integrate autonomic responses with emotional
state
Brain Stem and Spinal cord
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Visceral somatic information
Anatomic Considerations
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Inputs
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Hypothalamus also has intrinsic sensory
neurons
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Directly responsive to physical stimuli
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Temperature
Blood osmolality
Glucose
Anatomic Considerations
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Outputs
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Neural
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Reciprocate inputs
Hippocampus
Amygdala
Thalamus
Brain Stem
Spinal Cord
Hormonal
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Pituitary gland
Anatomic Considerations
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Two parts of the pituitary gland
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Neurohypophysis
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Direct neural control of hormone release into blood via
neurosecretory cells
Adenohypophysis
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Not a direct neural link
Vascular connection with hypothalamus
Anatomic Considerations
Adenohypophysis
Neurohypophysis
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Clinical Correlation
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Suprachiasmatic Nucleus
Center for circadian rhythm regulation
 Has a natural 25 hour set cycle
 Daylight cues and melatonin from the pineal
gland “train” it to a 24-hour cycle
 Important in sleep/wake cycle
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Clinical Correlation
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Mammillary Bodies
Part of the limbic Papez Circuit
 Crucial for memory function
 Mammillary bodies are damaged by chronic
alcohol abuse
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Clinical Correlation
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Clinical Correlation
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Long-term chronic alcoholics end up with
alcohol induced dementia
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Temporally graded severe memory loss
Clinical Correlation
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Motivation, reward and addiction
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Dr. Lester
Coming Up…
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Cytology - Dr. Lester
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I’ll reappear later in the course
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I am available for questions/clarifications
banos@uab.edu