Chapters 21 22 Single

Limbic System Forms a limbus (border) around the brainstem „ Emotional behavior and memory „

Limbic ‘Lobe’ Components

Limbic System Components „ „ „ „

Septal Nuclei Amygdala Hypothalamus (mamillary bodies) Thalamus … Anterior

nucleus … Medial nucleus

„ „ „ „ „

Reticular Formation Epithalamus Frontal cortex Olfactory cortex Ventral striatum

Limbic System Functions Emotional behavior „ Memory „ Homeostatic responses „

… Survival

instinct … Securing food … Fight or flight

Sexual behavior „ Motivation „

Hippocampal Formation Hippocampus „ Dentate gyrus „

… Toothed

surface „

Subiculum

Hippocampal Formation Hippocampus „ Dentate gyrus „ Subiculum „

Hippocampus „

Archicortex - 3 layers … Molecular … Pyramidal „

Compact zone …

„

Superior division

Less compact …

Inferior division

… Multiform

Hippocampus - Fields „

CA1 …

Superior … Sensitive to „ „

…

Temporal lobe epilepsy „

„

Trigger zone

CA2 & CA3 …

„

Anoxia Ischemia

Inferior region

CA4 …

Transition between hippocampus and dentate gyrus

Hippocampal Neurons „

Principal neurons …

Pyramidal … Output … Apical dendrites „

…

Basal dendrites „

…

Towards molecular layer Towards ventricular surface

Axons „ „

Ventricular surface Form … …

„

Alveus Fornix

Recurrent collaterals … … …

Molecular layer Multiform layer Excitatory

Hippocampal Neurons „

Intrinsic neurons … Polymorphic

neurons „

Irregularity of soma and dendrites

… Multiform

layer … Axons to pyramidal cells Arborize around body „ Aka basket cells „

… Inhibitory

Dentate Gyrus „

3 layers … Molecular … Granule

Small densely packed granule cells „ Form mossy fiber system „

…

Dentate gyrus to hippocampus

… Multiform „

Pyramidal …

„

Output to hippocampus

Basket cells

Subiculum „

3 layers … Molecular … Pyramidal „

Output through fornix

… Multiform

Hippocampal Formation: Afferents „ „ „ „ „ „ „ „ „

Entorhinal Septal area Contralateral hippocampus Hypothalamus Thalamus Amygdala Locus ceruleus Raphe nucleus Ventral tegmental area

Hippocampal Formation: Afferents „

Entorhinal area … Parahippocampal

gyrus to hippocampal formation … Perforant Pathway „

Perforates subiculum en route to hippocampus & dentate gyrus

… Alvear „ „

Pathway

Smaller Ventricular surface of the hippocampus, near the alveus

… Most

heavily damaged in Alzheimer’s … Site of early onset in Alzheimer’s

Hippocampal Formation: Efferents

Fornix „

Output of hippocampus …

Thalamus & hypothalamus … Septal region „

Pyramidal axons … … … … … …

…

Alveus Fimbria Crus of fornix Body of fornix Columns of fornix 75% synapse in mamillary bodies and anterior nucleus of the thalamus 25% synapse in septal nuclei

Entorhinal-Hippocampal Circuitry „

Excitatory synapses

Amygdala ‘almond’ shaped nuclei „ Tip of temporal lobe „

Amygdala: Afferents Olfactory, somatosensory, auditory, visual „ Autonomic inputs „ Integrates „

Amygdala: Efferents „

Stria terminalis … Main

output … Septal nuclei … Anterior, preoptic, ventromedial nuclei of the hypothalamus … Bed nucleus „

Scattered group of nuclei at the end of the stria terminalis

Amygdala: Efferents „

Ventral amygdalofugal pathway … … … … … …

Prefrontal, inferior temporal, insular, cingulate, occipital cortices Ventral striatum Dorsomedial nucleus of the thalamus Hypothalamus Septal area Substantia innominata „ „

…

Diffuse cholinergic system Activates cortex in response to significant stimuli

Brainstem nuclei involved in visceral functions „

Dorsol motor nucleus of the vagus, raphe nuclei, locus ceruleus, parabrachial nucleus, etc

Amygdala: Functions „

Autonomic …

„ „

…

„

…

„

„ „

Happiness, pleasure Hyperphagia

Sluggish, hypoactive

Sexual activity …

High density of sex hormone receptors … Bilateral lesions

Decreased emotional tone, fear sadness aggression Aphagia

Basolateral group

lesion: „

„

Mostly negative emotions

Arousal response …

Corticomedial group of nuclei „

Emotional & social meaning „

To novel events

Emotional behavior & food intake

Facial expression …

Heart rate, respiration, blood pressure, gastric motility

Orienting response …

„

„

„

Hypersexuality

Motor activity …

Related to eating

Septal Area „

2 divisions … Septum

pellucidum „ „

Glia Separates lateral ventricles

… Septum „ „ „

verum

Septal nuclei Bed nucleus Nucleus accumbens

Septal Area: Afferents & Efferents „

Reciprocal

Septal Area: Functions „

Emotional behavior …

Lesion „

„

Rage

Water Consumption …

Lesion „

Hyperactivity to novel stimulus, which quickly drops to immobility

Lesion „

„

Stimulation „

„

Learn quickly, perform effectiviely

Reward …

Over drink

Activity …

Learning …

Lesion „

„

„

Pleasure

Autonomic effects …

Stimulation „

Inhibit autonomic function …

Via vagus

Limbic Loop: Integrator Takes sensory processing and autonomic/endocrine information „ Modulates frontal processing „ Goal: to affect motor behavior „

Limbic System: Functions „

Preservation of the individual … Flight/fight

„ „ „

… Eating … Drinking

„

Preservation of the species … Sexual

behavior … Social behavior

„

Emotional behavior Memory Emotional valence of sensory stimuli Motivation

Memory „

Explicit/Declarative … Episodic

(personal experience) – limbic system … Semantic (knowledge) - neocortex … Short-term vs long-term „

Implicit … Procedural

(skill learning) – basal ganglia/cerebellum … Priming – sensory association areas „

„

Short-lived enhancement following recent exposure to similar material False memories/Deja vu

Clinical Correlates „

Amnesia … Retrograde … Anterograde … Global

– acute, transient severe anterograde with varying periods of retrograde … Modality-specific – e.g. vision … Permanent – e.g. Alzheimer’s … Transient – e.g. post-traumatic

Temporal Lobe Epilepsy „ „ „ „ „ „ „ „ „

Olfactory hallucinations, e.g. smelling burning rubber Gustatory hallucinations, e.g. bad taste Auditory hallucinations Visual hallucinations Rhythmic movements related to feeding Complex motor acts [walking, undressing] Amnesia Aggressive behavior Possibly death due to autonomic [cardiac] control

Alzheimer’s „ „

Degenerative Severe memory loss … Starts

as short-term, but accelerates as disease progresses

„ „

Disorientation to time, place, person Behavioral … Depression,

aggression

paranoia,

Alzheimer’s „

„

„ „ „ „

Shrunken gyri in association cortices and limbic system Primary sensory cortices and motor cortex mostly spared Neurofibrillary tangles (tau protein) Senile plaques (betaamyloid) Genetic form Environmental … Aluminum?