Ch 12-Limbic System + Language Disorders (Ch14)

Limbic System major functions:

• emotions

• memories

• (mostly declarative memory formation, memory consolidation, emotion memory, conditioning)

• arousal

• behaviors we need for survival; feeding, reproduction and caring for our young, and fight or flight responses

Limbic system “surrounds”:

basal ganglia & thalamus

BG & Thalamus

limbic system

Superior to corpus callosum

cingulate cortex

Cingulate Cortex

essential to emotional processing, learning, and memory

four parts of cingulate cortex

• anterior cingulate cortex

• midcingulate cortex

• posterior cingulate cortex

• retrosplenial cortex

part of temporal lobe

entorhinal cortex

entorhinal cortex

essential for memory and spatial navigation

works with hippocampal and parahippocampal cortices; pathway for sensory information to travel from the cortex to the hippocampus

entorhinal cortex

Implicated in Alzheimer’s Disease

entorhinal cortex

located mostly in temporal lobe

hippocampus

looks like a seahorse

hippocampus

hippocampus afferent & efferent areas

• afferents from cortex, olfactory areas, seuptum, hypothalamus

• efferents to amygdala, septum, hypothalamus, thalamus

hippocampus function

memory, learning, spacial navigation, emotional processing

hippocampal connectivity

parahippocampal gyrus

grey matter region of the brain that surrounds the hippocampus

contains the entorhinal cortex, which provides most of the input to the hippocampus

parahippocampal gyrus

Damage to bilateral hippocampal areas cause severe ______ problems

memory

clinical issues in hippocampus:

• alzheimer’s disease

• frontotemporal lobar disease

• related to recent memory and explicit memory

• episodic memory

• memory consolidation (encoding)

clinical issues to hippocampus

related to incoming words to stored semantic knowledge

hippocampus & language

hippocampal declarative memory system is long known to support ___________________. 

relational binding and representational flexibility 

recent findings demonstrate that these same functions are engaged during the real-time processes that support _______________. 

behavior in-the-moment

hippocampus as a potentially key contributor to cognitive functions that require on-line integration of multiple sources of information, such as _______________________.

on-line language processing

c-shaped fiber tract from hippocampus

• myelinated afferent & efferent fibers

• splits from hippocampus

• continues to anterior commissure

fornix

fornix function

episodic memory

fornix clinical issues:

• may relate to Alzheimer’s disease

• hypothesized to degenerate and amount of degeneration may relate to severity of cognitive impairment 

• relates environmental stimuli to coordinated behavior for autonomic and endocrine responses

• decision making

amygdala functions 

amygdala responses include:

• feeding

• fighting

• responses to stress 

• lesions=motivation problems

• apathy 

• flat affect

• inappropriate sexual behaviors and mouthing of objects

• loss of normal fear and anger responses 

clinical issues in amygdala

• difficulty with discrimination of emotional faces

• Kulver-Bucy syndrome

flat affect in amygdala

hypothalamus

central controller of homeostasis

• involved in autonomic control of endocrine system

• involved in emotions & motivated behavior

hypothalamus

HPA axis

Hypothalamic-Pituitary-Adrenal Axis

Hypothalamic-Pituitary-Adrenal Axis (what it is) 

major neuroendocrine system (cortisol)

Hypothalamic-Pituitary-Adrenal Axis (what it does) 

controls reactions to stress & regulates many body processes, including”

• digestion

• immune system

• mood and emotions 

• sexuality 

• energy storage and expenditure 

clinical issues in HPA axis:

• depends on area disturbed (e.g., lateral portion)

• reward & motivation

  • addiction

• stress responses

  • anxiety disorders

• feeding, reward

  • obesity

• composed of medial and lateral nuclei

• located at the ends of the anterior arches of the fornix

• cells in mammillary bodies are projection neurons

mammillary bodies

mammillary bodies

thought to encode spatial memory through connections with anterior thalamus

clinical issues in mammillary bodies

amnesia

Wernicke-Korsakoff’s sydrome

mammillary body atrophy is observed; a disorder characterized by amnesia and usually linked to a thiamine deficiency 

septal cortex

• pleasure center

• defensive reactions

• inhibition of heart rate

limbic blood supply

originates from several sources

main vessels that serve much of the limbic system:

• anterior cerebral artery (internal carotid)

• posterior cerebral artery (basilar artery)

• anterior choroidal artery (internal carotid)

• branches arising from the circle of willis 

amygdala, in conjunction with prefrontal cortex and medial temporal lobe, is involved in consolidation and retrieval of emotional memories. Amygdala, prefrontal cortex and hippocampus are also involved in the acquisition, extinction and recovery of fears to cues and contexts.

emotional memory

The components include the hippocampus and adjacent cortex, the parahippocampal regions (PHG), the entorhinal and perirhinal regions

• Involved in the creation & storage of new memories (consolidation)

• Memory is spatial and declarative

medial temporal lobe memory system

The diencephalic memory circuit consists of the hypothalamus, mammillary body and the dorsomedial nucleus of thalamus.

• Important for the storage of recent memory

• Dysfunction of this circuit results in Korsakoff's syndrome

diencephalic memory system

autonomic functions regulating heart rate and blood pressure as well as cognitive, attentional and emotional processing

cingulate gyrus

spacial memory

parahippocampal gyrus

long-term memory

hippocampus

anxiety, aggression, fear conditioning; emotional memory and social cognition

amygdala

regulates the autonomic nervous system via hormone production and release. Secondarily affects and regulates blood pressure, heart rate, hunger, thirst, sexual arousal and the circadian rhythm sleep/wake cycle

hypothalamus

memory

mammillary body

reward, addiction

nucleus accumbens

appetite, temperature and sleep disorders

hypothalamus

• affected in several neurologic disorders and psychiatric disorders including Alzheimer’s, temporal lobe epilepsy (TLE), anxiety, and depression

• symptoms manifest as impaired or unusual emotional behaviors in response to sensory stimuli, events, and memories (e.g. no threat response)

amygdala 

• Highly vulnerable area, so damaged in a variety of disorders (e.g., Alzheimer’s, TBI, epilepsy, etc) → it is so vulnerable because it is so plastic

• Issues in learning and memory (especially declarative memory – making new memories or losing old memories), can also manifest as issues in emotional response, spatial orientation,

hippocampus

damage to limbic lobe connections: 

• Psychiatric disorders: depression, schizophrenia, anxiety

• Addiction

• Issues in motivation and reward

Major fiber tracts

• Cingulum = projects from cingulate gyrus to entorhinal cortex

• Mamillothalamic tract = fibers connect MB to cingulate through anterior thalamic nucleus

• Fornix = connects hippocampus to septum, anterior thalamic nuclei, & mammillary body

neural tube →

prosencephalon

prosencephalon→

telencephalon & diencephalon

diencephalon→

thalamus, hypothalamus, retina

Diencephalon structures

• thalamus

• hypothalamus

• optic tract

• subthalamic nucleus

• epithalamus

  • habenulus

  • pineal glad

  • stria medullaris

thalamus structure

• bilateral structure 

  • one in each hemisphere; separated by the third ventricle

  • connection between thalami is at thalamic adhesion 

thalamus length

~3.5 cm long; size and shape of a walnut in its shell

thalamus is made up of groups of what?

subcortical nuclei (gray matter)

• bidirectional pathways connect between many cortical and subcortical areas

• involved in sensory, motor, limbic, reticular, conscious awareness, etc. 

thalamus receives blood from where?

branches of the posterior cerebral artery

thalamus afferent pathway orientation

from contralateral side of body; sensory information cross over prior to thalamus

thalamus efferent pathway orientation

from ipsilateral side of brain; motor information cross over after to thalamus

• most of the thalamic nuclei project to cerebral cortex 

• channels project sensation information (pain, taste, temperature, audition, and vision) to specific cortical areas

• takes in sensorimotor and cognitive information & projects info to appropriate areas of cortex 

  • behavior

  • memory

  • emotions

  • sleep-wake cycles

  • executive function

  • alertness  

thalamus function

Mediodorsal TN primary functions

mood, emotion, cognition, personality

Mediodorsal TN connections

hippocampus, cortical association areas, prefrotal, oribitofrontal, limbic, hippocampus, hypothalamus