Diencephalon, internal capsule & limbic system

Diencephalon

• Thalamus

• Epithalamus

• Subthalamus

• Hypothalamus

• Mammilary bodies

Boundaries of the diencephalon

Dorsal: Lateral ventricles

Laterally: Internal capsule

Medially: 3rd ventricle

Ventrally: Midbrain

Rosterally: Anterior commissure

Cadually: Posterior commissure

Papez Circuit

Limbic System

Fibres of the Internal Capsule

• Projection fibre tract (white matter axons)

• Both sensory (ascending) and motor (descending) neuron axons

• Anterior limb:

  • Corticopontine (motor)

  • Thalamocortical (sensory)

• Genu limb:

  • Corticobulbar (motor)

• Posterior limb:

  • Corticospinal (motor)

  • Corticobulbar (motor)

  • Thalamocortical (sensory)

Blood Supply of the Internal Capsule

• Anterior Limb

  • Anterior cerebral artery

• Genu Limb

  • Middle cerebral artery

• Posterior Limb

  • Anterior choroidal artery supply by internal carotids

Amygdala

• Fear and fear conditioning

• Emotional reactions such as fear, aggression or anger.

  • Learning that a neutral stimulus predicts the appearance of an aversive event.

  • Experimental stimulation most often elicits an anger or a fear response.

• Emotional learning and memory

• Anterior superior to hippocampus to add emotional response to a visual, auditory, olfactory etc inputs going into memory

• Reward processing: Processing of information that leads to positive emotions, and this affects our thinking and preferences

Epithalamus

• Pineal gland (size of a pea) and habenular nuclei

• The pineal gland is part of the endocrine system because it secretes

  • Melatonin in high concentrations in the darkness for sleepiness.

  • Pineal gland is also regulated by the suprachiasmatic nucleus.

Explicit Memory

• Memory of facts

• Declarative memory

• inferomedial aspects of the temporal lobes — in the hippocampus.

• Bilateral removal of medial portion of the temporal lobe (treat epilepsy) resulted in devastating declarative memory deficits

  • Recent and remote memory.

  • Could still learn certain tasks and retain this. (implicit/procedural memory)

• Conscious memory that can be classified as episodic (events and personal experience) or semantic (memory of facts e.g. learnt at school, and recognition of people)

Blood Supply of the Thalamus

Branching of posterior cerebral

• Thalamogeniculate Arteries

• Thalamoperforator Arteries

• Posterior communicating to connect it to the internal carotids

Lateral Division of the Thalamus

• Lateral dorsal: Expression

• Lateral posterior: Sensory

• Pulvinar: Sensory.

• Lateral ventral anterior: Basal ganglia cerebellum

• Lateral Ventral lateral: Basal ganglia, cerebellum

• Ventral posterolateral (body) + posteromedial (head)

• Internal medullary lamina of fibres divides

  • Medial geniculate (auditory)

  • Lateral geniculate (visual)

  • Midline = olfaction and memory

  • Encloses splits and closes anterior division

Other divisions of the thalamus (anterior, medial, intralaminar and reticular)

• Anterior division = anterior nucleus = emotion memory

• Medial division = Dorsomedial nucleus = learning memory cognition

• External medullary lamina

• Reticular division inhibits other thalamic nuclei

• Intralaminar nuclei are within the internal medullary lamina connecting reticular formation, cerebellum, basal ganglia, cortex pain perception

Hypothalamus

• Regulates 6 basic physiological needs (homeostasis)

• Releases tropic hormones to regulate the anterior pituitary (adenohypophysis - produces hormones)

• Synthesises hormones that are stored in the posterior pituitary (neurohypophysis).

• Output along the hypothalamospinal fibre tracts to control autonomic motor output - autonomic control

• Somatic motor output (behavioural responses)

• 4g

Tropic hormone

• Secreted by one endocrine gland

• Travels in the blood to another endocrine gland

• Affects hormone release of that gland

Relationship between the anterior pituitary and hypothalamus - ADD

Divisions of the hypothalamus

• Lateral and medial zones: extensive connections
  with the brainstem and telencephalon

• The periventricular zone: lies next to the 3rd
  ventricle and receives much of its inputs from
  the medial and lateral zones

Septal area

• A group of nuclei for pleasurable states and reward mechanisms.

• Experimental animals press a lever repeatedly to obtain electrical stimulation of the septal area to the point of neglecting to eat.

• Lesions of the septal area in animals cause "sham rage," sudden outbursts of aggressive behaviour.

Nucleus Accumbens

• Processing emotion and reward/addiction.

• When something is rewarding or pleasurable, dopamine is released and sends signals to the nucleus accumbens, reinforcing the behaviour

• Large inputs from brainstem dopaminergic neurons, the hippocampus, and the amygdala.