The Diencephalon

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

2. Overview • Parts of the diencephalon • Thalamus • Hypothalamus

3. The Diencephalon

4. The Diencephalon • Four major parts: • Epithalamus • Dorsal Thalamus • Subthalamus • Hypothalamus

5. The Diencephalon • Epithalamus • Pineal gland • A few nearby structures Pineal Gland

6. 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

7. Clinical Correlation • What did Descartes think?

8. Clinical Correlation

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

10. The Diencephalon • Dorsal Thalamus • Thalamic hemispheres • 80% of diencephalon

11. The Diencephalon • Subthalamus • Zona incerta • Subthalamic nucleus

12. The Diencephalon • Hypothalamus

13. The Diencephalon • Hypothalamus Optic Chiasm Infundibulum Mammilary Bodies

14. The Diencephalon • Hypothalamus Mammilary Bodies Optic Chiasm Infundibulum

15. Dorsal Thalamus

16. 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

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

18. 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

19. 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

20. Anterior Medial Lateral See p. 395

21. Anatomical Divisions • Anterior 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)

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

23. LD A Pulv DM VL A Ret CM PF VPL VL VA VPM MGN LGN Pulv DM VPL A VL VA Ret See p. 395

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

25. 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

26. Functional Divisions • Relay Nuclei • Anterior & Lateral Dorsal (LD) • Hippocampus to Cingulate Gyrus • Ventral Anterior (VA)/Ventral Lateral (VL) • Basal Ganglia/cerebellum to motor areas • Ventral Posterolateral (VPL) • Medial Lemniscus & Spinothalamic Tract to somatosensory cortex (body) • Ventral posteromedial (VPM) • Medial Lemniscus & Spinothalamic Tract to somatosensory cortex (face)

27. Functional Divisions • Relay Nuclei • Medial Geniculate (MGN) • Inferior colliculus to auditory cortex • Lateral Geniculate (LGN) • Optic Tract to visual cortex

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

29. Other Nuclei • Intralaminar nuclei • Inputs are diverse! • Cortex, basal ganglia, cerebellum, brainstem reticular formation, spinothalamic tract • Project to • Widespread areas of cortex • Basal ganglia • Produce general changes in cortical function • Arousal • Alertness • Cortical “tone”

30. 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

31. Clinical Correlation • Thalamic Stroke - What’s the number one symptom you might predict?

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

33. 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

34. Hypothalamus

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

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

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

38. 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

39. Anatomic Considerations • Can be divided into three regions • Each region includes medial and lateral zones • Medial and Lateral include Periventricular Zone also Posterior Anterior Tuberal

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

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

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

43. 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

44. Anatomic Considerations Adenohypophysis Neurohypophysis

45. 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

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

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

48. Clinical Correlation • Motivation, reward and addiction • Dr. Lester

49. Coming Up… • Lab! • I’ll reappear later in the course • I am available for questions/clarifications banos@uab.edu