The Diencephalon Basic Neuroscience James H. Baños, Ph.D.

Overview Parts of the diencephalon Thalamus Hypothalamus

The Diencephalon

The Diencephalon Four major parts: Epithalamus Dorsal Thalamus Subthalamus Hypothalamus

The Diencephalon Epithalamus Pineal gland A few nearby structures

The Diencephalon Pineal Gland 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 What did Descartes think?

Clinical Correlation

Clinical Correlation Pineal Tumor Hydrocephalus. Why? Eye movement abnormalities. Why?

The Diencephalon Dorsal Thalamus Thalamic hemispheres 80% of diencephalon

The Diencephalon Subthalamus Zona incerta Subthalamic nucleus

The Diencephalon Hypothalamus

The Diencephalon Hypothalamus Mammilary Bodies Infundibulum

Dorsal Thalamus

Functional Roles Thalamus has four basic functional roles: Sensory All sensory information (except olfaction) is relayed to the cortex via the thalamus Motor Motor system outputs from the basal ganglia and cerebellum are relayed by the thalamus Emotion/memory The thalamus is part of the Papez circuit and helps control some emotional and memory information going to limbic cortex (cingulate gyrus) Vegetative The thalamus has some intrinsic nuclei associated with alertness and arousal. Can be associated with disorders of consciousness

Thalamus Trivia!! What is the single largest source of input to the thalamus?

Functional Roles 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

Anatomic Divisions Internal medullary lamina Thin sheet of myelinated fibers Divides the thalamus into four major divisions, each containing specific nuclei: Anterior Medial Lateral Not included in these divisions are The intralaminar nuclei The Reticular nucleus

Anterior Medial Lateral See p. 392

Anatomical Divisions Anterior Division Medial Division Anterior nucleus Medial Division Dorsomedial Nucleus (DM) Lateral Division Dorsal Tier Lateral dorsal (LD) Lateral Posterior (LP) Pulvinar Ventral Tier Ventral Anterior (VA) Ventral Lateral (VL) Ventral Posterior (VP) Ventral posteriolateral (VPL) Ventral posteriomedial (VPM)

Anatomical Divisions …But wait…there’s more… Medial Geniculate Nucleus (MGN) Lateral Geniculate Nucleus (LGN) Intralaminar Nuclei Centromedian (CM) Parafascicular (PF) Reticular Nucleus

A VA VL DM VPL VPM CM PF Pulv MGN LGN Ret LD See p. 392

Functional Divisions Another way to think of this Relay nuclei (i.e., relay to the cortex) Association nuclei “Other” nuclei Interlaminar Reticular

Functional Divisions

Functional Divisions Relay Nuclei Relay specific information from a particular tract or modality This is not just sensory information Relay nuclei are part of several important modulatory loops in the CNS This is not simple “passing on” of the signal Relay nuclei engage in some complex condensing and processing of the incoming raw information

Functional Divisions Association nuclei Support areas of association cortex Prefrontal cortex Parietal-occipital-temporal cortex Association cortex is involved in higher cognitive function

Other Nuclei Intralaminar nuclei Inputs are diverse! Project to Cortex, basal ganglia, cerebellum, brainstem reticular formation, spinothalamic tract Project to Widespread areas of cortex Basal ganglia Produce general changes in cortical function

Other Nuclei Reticular nucleus 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 Thalamic Stroke - What’s the number one symptom you might predict?

Clinical Correlation Thalamic Stroke Loss of consciousness/coma Attention/arousal problems Widespread disruption of cortical function Severe cognitive deficits

Clinical Correlation Anterior nucleus Part of the Papez Circuit in the limbic system Involved in memory Unilateral Damage: Encoding deficit Bilateral Damage: Severe encoding deficit

Hypothalamus

Hypothalamus Caudate Ventricle Thalamus Hypothalamus Putamen & Globus pallidus Hypothalamus Amygdala

Hypothalamus Pituitary Stalk

Hypothalamus Hypothalamus Coordinates Drive-Related Behaviors What are “Drive-related behaviors?”

Hypothalamus Behaviors follow the principal of homeostasis “Drive” refers to drive to correct homeostatic imbalance Hunger/satiety Thirst Sexual behavior Temperature regulation Sleep

Hypothalamus Hypothalamus is also the integrative link between the external and internal environment External Environment Hypothalamus Internal Environment

Hypothalamus 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) The position of the hypothalamus is not a coincidence

Anatomic Considerations Can be divided into three regions Each region includes medial and lateral zones Posterior Anterior Tuberal

Anatomic Considerations Three regions X two zones = six areas containing nuclei

Anatomic Considerations See p. 563

Anatomic Considerations Inputs Widespread! Cortex Limbic system Helps integrate autonomic responses with emotional state Brain Stem and Spinal cord Visceral somatic information

Anatomic Considerations Inputs Hypothalamus also has intrinsic sensory neurons Directly responsive to physical stimuli Temperature Blood osmolality Glucose

Anatomic Considerations Outputs Neural Reciprocate inputs Hippocampus Amygdala Thalamus Brain Stem Spinal Cord Hormonal Pituitary gland

Anatomic Considerations Two parts of the pituitary gland Neurohypophysis Direct neural control of hormone release into blood via neurosecretory cells Adenohypophysis Not a direct neural link Vascular connection with hypothalamus

Anatomic Considerations Adenohypophysis Neurohypophysis

Clinical Correlation 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

Clinical Correlation Mammillary Bodies Part of the limbic Papez Circuit Crucial for memory function Mammillary bodies are damaged by chronic alcohol abuse

Clinical Correlation

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

Clinical Correlation Motivation, reward and addiction Dr. Lester

Coming Up… Cytology - Dr. Lester I’ll reappear later in the course I am available for questions/clarifications banos@uab.edu