The Diencephalon

The DiencephalonThe Diencephalon

Basic NeuroscienceBasic Neuroscience

James H. Baños, Ph.D.James H. Baños, Ph.D.

OverviewOverview

Parts of the diencephalonParts of the diencephalon ThalamusThalamus HypothalamusHypothalamus



Four major parts:Four major parts: EpithalamusEpithalamus Dorsal ThalamusDorsal Thalamus SubthalamusSubthalamus HypothalamusHypothalamus


EpithalamusEpithalamus Pineal glandPineal gland A few nearby A few nearby

structuresstructures

Pineal Gland


Pineal GlandPineal Gland Unpaired midline structureUnpaired midline structure Just rostral to superior colliculiJust rostral to superior colliculi Looks like a pine cone (“pineal”)Looks like a pine cone (“pineal”) Endocrine gland related to seasonal light Endocrine gland related to seasonal light

cyclescycles Secretes melatonin Secretes melatonin

Clinical CorrelationClinical Correlation

What did Descartes think?What did Descartes think?



Pineal TumorPineal Tumor Hydrocephalus. Why?Hydrocephalus. Why? Eye movement abnormalities. Why?Eye movement abnormalities. Why?


Dorsal ThalamusDorsal Thalamus Thalamic Thalamic

hemisphereshemispheres 80% of 80% of

diencephalondiencephalon


SubthalamusSubthalamus Zona incertaZona incerta Subthalamic Subthalamic

nucleusnucleus


HypothalamusHypothalamus



Mammilary Bodies

Infundibulum

Optic Chiasm



Mammilary Bodies

Infundibulum

Optic Chiasm

Dorsal ThalamusDorsal Thalamus

Functional RolesFunctional Roles Thalamus has four basic functional roles:Thalamus has four basic functional roles:

SensorySensory All sensory information (except olfaction) is relayed to the All sensory information (except olfaction) is relayed to the

cortex via the thalamuscortex via the thalamus MotorMotor

Motor system outputs from the basal ganglia and Motor system outputs from the basal ganglia and cerebellum are relayed by the thalamuscerebellum are relayed by the thalamus

Emotion/memoryEmotion/memory The thalamus is part of the Papez circuit and helps control The thalamus is part of the Papez circuit and helps control

some emotional and memory information going to limbic some emotional and memory information going to limbic cortex (cingulate gyrus)cortex (cingulate gyrus)

VegetativeVegetative The thalamus has some intrinsic nuclei associated with The thalamus has some intrinsic nuclei associated with

alertness and arousal. Can be associated with disorders of alertness and arousal. Can be associated with disorders of consciousnessconsciousness

Thalamus Trivia!!Thalamus Trivia!!

What is the single largest source of What is the single largest source of input to the thalamus?input to the thalamus?

Functional RolesFunctional Roles

Thalamus doesn’t just send Thalamus doesn’t just send information to the cortex. It receives information to the cortex. It receives cortical feedbackcortical feedback This signal helps regulate what is coming This signal helps regulate what is coming

to the cortexto the cortex Cortical input is a feedback inhibition Cortical input is a feedback inhibition

looploop, letting the thalamus know that , letting the thalamus know that information has been received and information has been received and inhibiting further relaying of the inhibiting further relaying of the informationinformation

Anatomic DivisionsAnatomic Divisions

Internal medullary laminaInternal medullary lamina Thin sheet of myelinated fibersThin sheet of myelinated fibers Divides the thalamus into four major Divides the thalamus into four major

divisions, each containing specific nuclei:divisions, each containing specific nuclei: AnteriorAnterior MedialMedial LateralLateral

Not included in these divisions areNot included in these divisions are The The intralaminar nucleiintralaminar nuclei The The Reticular nucleusReticular nucleus

See p. 395

Anterior

Medial

Lateral

Anatomical DivisionsAnatomical Divisions

Anterior DivisionAnterior Division Anterior nucleusAnterior nucleus

Medial DivisionMedial Division Dorsomedial Nucleus (DM)Dorsomedial Nucleus (DM)

Lateral DivisionLateral Division Dorsal TierDorsal Tier

Lateral dorsal (LD) Lateral dorsal (LD) Lateral Posterior (LP)Lateral Posterior (LP) PulvinarPulvinar

Ventral TierVentral Tier Ventral Anterior (VA)Ventral Anterior (VA) Ventral Lateral (VL)Ventral Lateral (VL) Ventral Posterior (VP)Ventral Posterior (VP)

Ventral posteriolateral (VPL)Ventral posteriolateral (VPL) Ventral posteriomedial (VPM)Ventral posteriomedial (VPM)

Anatomical DivisionsAnatomical Divisions

……But wait…there’s more…But wait…there’s more…

Medial Geniculate Nucleus (MGN)Medial Geniculate Nucleus (MGN) Lateral Geniculate Nucleus (LGN)Lateral Geniculate Nucleus (LGN) Intralaminar NucleiIntralaminar Nuclei

Centromedian (CM)Centromedian (CM) Parafascicular (PF)Parafascicular (PF)

Reticular NucleusReticular Nucleus

A

VA VL

DMVL

VPLVPM

CMPF

A Pulv

MGN

LGN

Ret

LD

A

DMPulv

VPLVL

VARet

See p. 395

Functional DivisionsFunctional Divisions

Another way to think of thisAnother way to think of this Relay nuclei (i.e., relay to the cortex)Relay nuclei (i.e., relay to the cortex) Association nucleiAssociation nuclei ““Other” nucleiOther” nuclei

InterlaminarInterlaminar ReticularReticular


Relay NucleiRelay Nuclei Relay specific information from a particular Relay specific information from a particular

tract or modalitytract or modality This is This is notnot just sensory information just sensory information

Relay nuclei are part of several important Relay nuclei are part of several important modulatory modulatory loopsloops in the CNS in the CNS

This is not simple “passing on” of the This is not simple “passing on” of the signalsignal

Relay nuclei engage in some complex Relay nuclei engage in some complex condensing and processing of the incoming raw condensing and processing of the incoming raw informationinformation


Relay NucleiRelay Nuclei Anterior & Lateral Dorsal (LD)Anterior & Lateral Dorsal (LD)

Hippocampus to Cingulate GyrusHippocampus to Cingulate Gyrus Ventral Anterior (VA)/Ventral Lateral (VL)Ventral Anterior (VA)/Ventral Lateral (VL)

Basal Ganglia/cerebellum to motor areasBasal Ganglia/cerebellum to motor areas Ventral Posterolateral (VPL)Ventral Posterolateral (VPL)

Medial Lemniscus & Spinothalamic Tract to Medial Lemniscus & Spinothalamic Tract to somatosensory cortex (body)somatosensory cortex (body)

Ventral posteromedial (VPM)Ventral posteromedial (VPM) Medial Lemniscus & Spinothalamic Tract to Medial Lemniscus & Spinothalamic Tract to

somatosensory cortex (face)somatosensory cortex (face)


Relay NucleiRelay Nuclei Medial Geniculate (MGN)Medial Geniculate (MGN)

Inferior colliculus to auditory cortexInferior colliculus to auditory cortex Lateral Geniculate (LGN)Lateral Geniculate (LGN)

Optic Tract to visual cortexOptic Tract to visual cortex


Association nucleiAssociation nuclei Support areas of Support areas of association cortexassociation cortex

Prefrontal cortexPrefrontal cortex Parietal-occipital-temporal cortexParietal-occipital-temporal cortex

Association cortex is involved in higher Association cortex is involved in higher cognitive functioncognitive function

Other NucleiOther Nuclei

Intralaminar nucleiIntralaminar nuclei Inputs are diverse!Inputs are diverse!

Cortex, basal ganglia, cerebellum, brainstem Cortex, basal ganglia, cerebellum, brainstem reticular formation, spinothalamic tract reticular formation, spinothalamic tract

Project to Project to Widespread areas of cortexWidespread areas of cortex Basal gangliaBasal ganglia

Produce general changes in cortical Produce general changes in cortical functionfunction

ArousalArousal AlertnessAlertness Cortical “tone”Cortical “tone”

Other NucleiOther Nuclei

Reticular nucleusReticular nucleus Sheet-like layer of neurons partially covering Sheet-like layer of neurons partially covering

the thalamusthe thalamus Receives input from widespread cortical areasReceives input from widespread cortical areas Only thalamic nucleus with Only thalamic nucleus with nono projections to projections to

the cortexthe cortex Inhibitory projections to specific thalamic Inhibitory projections to specific thalamic

nucleinuclei Regulates the activity of the thalamus in the Regulates the activity of the thalamus in the

form of cortical feedback form of cortical feedback


Thalamic Stroke - What’s the Thalamic Stroke - What’s the number one symptom you might number one symptom you might predict?predict?


Thalamic StrokeThalamic Stroke Loss of consciousness/comaLoss of consciousness/coma Attention/arousal problemsAttention/arousal problems Widespread disruption of cortical Widespread disruption of cortical

functionfunction Severe cognitive deficitsSevere cognitive deficits


Anterior nucleusAnterior nucleus Part of the Papez Circuit in the limbic Part of the Papez Circuit in the limbic

systemsystem Involved in memoryInvolved in memory Unilateral Damage: Encoding deficit Unilateral Damage: Encoding deficit Bilateral Damage: Bilateral Damage: SevereSevere encoding encoding

deficitdeficit



Hypothalamus Coordinates Drive-Hypothalamus Coordinates Drive-Related BehaviorsRelated Behaviors

What are “Drive-related behaviors?”What are “Drive-related behaviors?”


Behaviors follow the principal of Behaviors follow the principal of homeostasishomeostasis

““Drive” refers to drive to correct Drive” refers to drive to correct homeostatic imbalancehomeostatic imbalance Hunger/satietyHunger/satiety ThirstThirst Sexual behaviorSexual behavior Temperature regulationTemperature regulation SleepSleep


Hypothalamus is also the integrative Hypothalamus is also the integrative link between the external and link between the external and internal environmentinternal environment

Internal Environment

External Environment

Hypothalamus


Interaction with external environment Interaction with external environment occurs through integration with the occurs through integration with the cortexcortex

Interaction with the internal Interaction with the internal environment occurs through:environment occurs through: ““Sampling” of blood and CSFSampling” of blood and CSF Release of hormones (via the pituitary)Release of hormones (via the pituitary)

The position of the hypothalamus is The position of the hypothalamus is not a coincidencenot a coincidence

Anatomic ConsiderationsAnatomic Considerations Can be divided into three regionsCan be divided into three regions Each region includes medial and lateral zonesEach region includes medial and lateral zones Medial and Lateral include Periventricular Zone Medial and Lateral include Periventricular Zone

alsoalso

Anterior

Tuberal

Posterior

Anatomic ConsiderationsAnatomic Considerations

InputsInputs Widespread!Widespread!

CortexCortex Limbic systemLimbic system

Helps integrate autonomic responses with Helps integrate autonomic responses with emotional stateemotional state

Brain Stem and Spinal cordBrain Stem and Spinal cord Visceral somatic informationVisceral somatic information


InputsInputs Hypothalamus also has intrinsic sensory Hypothalamus also has intrinsic sensory

neuronsneurons Directly responsive to physical stimuliDirectly responsive to physical stimuli

TemperatureTemperature Blood osmolalityBlood osmolality GlucoseGlucose


OutputsOutputs NeuralNeural

Reciprocate inputsReciprocate inputs HippocampusHippocampus AmygdalaAmygdala ThalamusThalamus Brain StemBrain Stem Spinal CordSpinal Cord

HormonalHormonal Pituitary glandPituitary gland


Two parts of the pituitary glandTwo parts of the pituitary gland NeurohypophysisNeurohypophysis

Direct neural control of hormone release into blood Direct neural control of hormone release into blood via neurosecretory cellsvia neurosecretory cells

AdenohypophysisAdenohypophysis Not a direct neural linkNot a direct neural link Vascular connection with hypothalamusVascular connection with hypothalamus


Adenohypophysis

Neurohypophysis


Suprachiasmatic NucleusSuprachiasmatic Nucleus Center for circadian rhythm regulationCenter for circadian rhythm regulation Has a natural 25 hour set cycleHas a natural 25 hour set cycle Daylight cues and melatonin from the Daylight cues and melatonin from the

pineal gland “train” it to a 24-hour cyclepineal gland “train” it to a 24-hour cycle Important in sleep/wake cycleImportant in sleep/wake cycle


Mammillary BodiesMammillary Bodies Part of the limbic Papez CircuitPart of the limbic Papez Circuit Crucial for memory functionCrucial for memory function Mammillary bodies are damaged by Mammillary bodies are damaged by

chronic alcohol abusechronic alcohol abuse


Long-term chronic alcoholics end up Long-term chronic alcoholics end up with alcohol induced dementiawith alcohol induced dementia Temporally graded severe memory lossTemporally graded severe memory loss


Motivation, reward and addictionMotivation, reward and addiction Dr. LesterDr. Lester

Coming Up…Coming Up…

Lab!Lab!

I’ll reappear later in the courseI’ll reappear later in the course

I am available for I am available for questions/clarificationsquestions/clarifications

[email protected]@uab.edu

Documents

The Diencephalon