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

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
Mammilary Bodies
Infundibulum

14. Dorsal Thalamus

15. 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

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

17. 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

18. 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

19. Anterior
Medial
Lateral
See p. 392

20. 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)

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

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

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

24. Functional Divisions

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

27. 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

28. 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

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

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

31. 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

32. Hypothalamus

33. Hypothalamus Caudate Ventricle Thalamus Hypothalamus Putamen &
Globus pallidus
Hypothalamus
Amygdala

34. Hypothalamus
Pituitary Stalk

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
Posterior
Anterior
Tuberal

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

41. Anatomic Considerations
See p. 563

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

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

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

45. 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

46. Anatomic Considerations
Adenohypophysis
Neurohypophysis

47. 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

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

49. Clinical Correlation

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

51. Clinical Correlation
Motivation, reward and addiction
Dr. Lester

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