Download REVIEW OF LIMBIC SYSTEM, HYPOTHALAMUS, THALAMUS

REVIEW OF
LIMBIC SYSTEM,
HYPOTHALAMUS,
THALAMUS, CORTEX
Dr. G.R. Leichnetz
Hippocampus
Hippocampal Formation:
Hippocampus Proper + Dentate Gyrus + Subiculum
The subiculum is a transition region between paleo- and archi-cortex.
CA2
CA3
Hippocampus Dentate gyrus
proper
CA1
Fimbria
of fornix
Subiculum
Hippocampal
Formation
The hippocampus proper consists of
CA1-CA3 subfields.
The dentate gyrus consists of CA4 plus
the “dentate fascia,” ie. molecular and
granular layers of the dentate gyrus.
Entorhinal
cortex
Hippocampal Connections:
Principal Afferents: Entorhinal Cortex
Principal Efferents:
Fornix
The entorhinal cortex
receives major
multimodal input
(somatosensory,
visual, auditory)
from associational
cortex, and relays
that information into
the hippocampus for
memory processing.
Prefrontal
assoc. cortex
Temporal
assoc. cortex
Parieto-occipital
assoc. cortex
Entorhinal
Afferents
The precommissural fornix terminates in the septum/
basal forebrain region. The postcommissural fornix
projects to hypothalamus, mammillary body, and
paramedian midbrain reticular formation (midbrain
limbic area, raphe).
The fornix to the mammillary body is the first segment
of “Papez Circuit,” followed by the mammillothalamic
tract to anterior nucleus of thalamus, cingulate gyrus,
and cingulum bundle to hippocampus.
Cingulate gyrus
cingulum
Ant. Nuc.
MTT
Mamm.
Body
Hippoc.
fornix
Bilateral lesions of
the hippocampus
produce
anterograde
amnesia, an
inability to learn
new information.
Past memories
largely intact.
The CA1 subfield
(Sommer’s sector)
is vulnerable to
vascular injury.
Wernicke’s encephalopathy (from a vitamin B1 thiamin
deficiency) produces focal vascular hemorrhages in
structures associated with Papez circuit (eg.
mammillary bodies, anterior nucleus of thalamus)
and results in Korsakoff’s syndrome with
anterograde amnesia.
Amygdala
The amygdala is located in the ventromedial temporal
lobe (rostral to the hippocampus) within the rostral
parahippocampal gyrus.
C
The amygdala consists of
numerous subnuclei, and
thus is referred to as the
“amygdaloid complex”.
MEDIAL
LATERAL
AMYGDALOID AFFERENTS
1. Multimodal Sensory Inputs- via relay in
adjacent temporal cortex, informs the
amygdala about ongoing sensory experience
2. Direct Olfactory Input- from olfactory bulb
Normal sensory “percepts” interact with
the amygdala to be “tagged” with an
appropriate emotional or motivational
significance.
AMYGDALOID EFFERENTS
Cortical EfferentsThe amygdala has feedback projections to
multimodal associational cortex (eg. prefrontal,
parietal, temporal) to bring “emotional salience” to
ongoing sensory experience (enhances attention).
From: Purves et al
AMYGDALOID EFFERENTS
Subcortical Efferentsvia stria terminalis & ansa peduncularis to:
Hypothalamus- feeding/appetite, reproductive behavior,
endocrine releasing factors
Mediodorsal nucleus of thalamus- relay to prefrontal
cortex (for emotional effects on mood personality, social
behavior, working memory)
Basal forebrain (nuc. accumbens)- addiction, pleasure/
reward
Brainstem autonomic nuclei- effects on autonomics
(cardiac, respiratory)
“Tagging” behaviors with emotion
The amygdala receives direct olfactory input, and other
multimodal (visual, auditory, somatosensory) input via
relay in adjacent temporal cortex. Its subcortical
efferents follow two paths: stria terminalis and ansa
peduncularis.
Noback
AMYGDALOID LESION
Amygdaloid stimulation produces aggression
Temporal lobe lesions which involve the amygdala
result in Kluver-Bucy Syndrome, producing lack of
emotion, fear; inability to discriminate between food
and non-food objects, hypersexuality.
(fundamentally this is an inability to comprehend the emotional
significance of objects, so they use them inappropriately)
Septum/ Basal Forebrain
The precommissural septum is a small gyrus in the
caudal frontal lobe, rostral to the anterior commissure.
It is a major nexus of the limbic system with the basal
ganglia.
Fornix
AC
Hypothalamus
MB
The precommissural septum is contiguous with the
basal forebrain. The septum/basal forebrain region
contains the nucleus accumbens and numerous
cholinergic nuclei (Ch1-Ch4).
Caudate
Putamen
S
Ch1Ch3
Ch4
Nucleus
basalis
NA
Basal forebrain
The nucleus accumbens is the largest nucleus of the
septum/basal forebrain, and is the “center for addiction.”
It receives the DA mesolimbic “reward system” from the
ventral tegmental area of the midbrain.
C
IC
P
ACC
Basal forebrain
S
The mesolimbic and mesocortical tracts, which
originate from the VTA (A10) traverse the medial
forebrain bundle in the lateral hypothalamus to reach
the nucleus accumbens and prefrontal cortex.
PFC
ACC
Mesocortical
VTA
Mesolimbic
Traverse the
medial forebrain
bundle
The nucleus accumbens has been called a “center for
addiction.”
It receives the major dopaminergic “reward system”
(mesolimbic) projections from the ventral tegmental
area of the midbrain. Its neurons have receptors to
most chemical substances of abuse (opioids, nicotine),
but also is activated by other pleasurable experiences
(eg. food, even music).
Amygdaloid projections to accumbens bring
“emotional” component to addiction.
Functional MRI studies show that the amygdala and nucleus
accumbens are activated even in the absence of cocaine if the
subject “imagines” the emotional high.
The medial forebrain bundle
carries afferents to, and
efferents from, the septum/
basal forebrain.
MFB
LC
Ascending NE projections from
the locus ceruleus (A6) and cell
groups A5, A7 traverse the MFB
MFB
CELL GROUPS
A5, A7
MFB
MIDBRAIN
RAPHE
(B7,B8)
Ascending 5-HT (serotonergic)
projections from the midbrain
raphe traverse the MFB
SEPTUM/BASAL FOREBRAIN
Afferents
Medial Forebrain Bundle (DA, NE, 5-HT)
Fornix (from hippocampus)
Stria terminalis, ansa peduncularis (from amygdala)
Efferents
Medial Forebrain Bundle (ACh) (to hypothalamus,
and brainstem
Reciprocal thru fornix (to hippocampus) and
stria terminalis, ansa peduncularis (to amygdala)
ACh projections (Ch4)- to cerebral cortex
The medial forebrain bundle carries cholinergic
projections from nuclei in the septum/basal forebrain
(Ch1-Ch3) to the hypothalamus and brainstem
reticular formation.
Medial forebrain bundle
Ch1-Ch3)
From: Niewenhuys, The Human Nervous System
The nucleus basalis of Meynert (Ch4), located in the
basal forebrain, is the principal source of cholinergic
innervation of the cerebral cortex. This nucleus shows a
profound loss of neurons in Alzheimer’s disease.
Ch4
Prefrontal Cortex
The prefrontal cortex is the
“neocortical representative of the
limbic system.”
It receives major limbic input
from the amygdala via the MD
nucleus of the thalamus.
It is involved in “working
memory,” and complex behavioral
responses where the individual
considers the consequences of
his/her actions.
“Strategy for behavior”
Lesion: perseveration, anti-social
behavior, mood & personality
aberrations
The prefrontal
cortex receives a
major input from
the mediodorsal
(MD) nucleus of
the thalamus,
which conveys
limbic influence
from the
amygdala.
PFC
MD
The “delayed response test” has classically been a
used to evaluate prefrontal function, eg. after brief
delay period, food reward changes compartments
Lesions result in perseveration.
Cannot alter behavioral strategy.
Working memory refers to the process of actively
maintaining relevant information in mind for brief
periods of time.
Prefrontal Functions:
Executive functions- cognition, decision-making
Working memory
Social behavior
Modified from Purves
Hypothalamus
Hypothalamus
Anterior
region
Tuberal
region
Posterior
region
The hypothalamus is
located in the ventral
diencephalon, and is a
collection of subnuclei
involved in higher-level
(the most complex)
autonomic,
visceroendocrine
functions.
The anterior region (preoptic
area) merges into the basal
forebrain. The tuberal region
are nuclei grouped over the
tuber cinereum (median
meinence). The posterior
region includes the
mammillary nuclei.
The principal afferents of the hypothalamus come from
the hippocampus (fornix), amygdala (stria terminalis
and ansa peduncularis), and septum/basal forebrain
(medial forebrain bundle).
Stria terminalis
Fornix
Medial forebrain
bundle
Septum/ Basal
Forebrain
Amygdala
Hippocampus
The hypothalamus receives major input from the
amygdala thru the stria terminalis and ansa peduncularis
through which emotion affects hypothalamic functions.
Noradrenergic (NE) cell groups (A1-A5, A7) in
the lateral pontine and medullary reticular
formation project to the hypothalamus.
Hypothalamus
A1-A5, A7
Hypothalamus:
Function of
Particular Nuclei
Direct projections from the retina to the hypothalamus;
to the suprachiasmatic nucleus, the “biological clock”
responsible for the brain’s circadian rhythmicity.
It
receives direct retinal input.
Suprachiasmatic
nucleus
Optic Chiasm
The supraoptic and
paraventricular nuclei of the
hypothalamus produce
vasopressin (ADH) and
oxytocin which are
transported through the
axons of the hypothalamohypophyseal tract to be
released in the posterior lobe
of the pituitary
(neurohypophysis).
PV
SO
Paraventricular nucleus
Supraoptic nucleus
RF-producing
cell groups end
in the arcuate
nucleus
Intrinsic hypothalamic
neurons that synthesize
“releasing factors”
terminate in the
arcuate nucleus of the
median eminence, and
RF’s reach the
anterior lobe of the
pituitary
(adenohypophysis) via
the hypothalamohypophyseal portal
system.
The ventromedial
nucleus of the
hypothalamus functions
as a “satiety center.”
VMH
Lesion of the
ventromedial nucleus of
the hypothalamus
results in hypothalamic
obesity.
Hypothalamic
obesity
Thalamus
The internal medullary lamina of the thalamus divides
the thalamus into medial and lateral nuclear groups.
The lateral nuclear group is subdivided into dorsal and
ventral tiers (containing specific relay nuclei).
The thalamus is the
principal source of
cortical afferents
(corticopetal projections).
All thalamocorticals are
glutamatergic
(excitatory).
The ventral tier of the
lateral group contains
the specific relay nuclei.
VA- from GP; to SMA (area 6) VLfrom cerebellum to area 4 VPfrom SL, ML; to area 3,1,2 LGNfrom OT; to area 17 MGN- from
IC, br. IC to areas 41,
42
A- from MTT; to cingulate gyrus
MD- from amygdala to PFC
Basic Pattern Of Thalamic Connections
Thalamocorticals
Corticothalamics
Thalamus
All thalamic nuclei
(except the
thalamic reticular
nucleus) have
reciprocal
connections with
the cerebral
cortex.
Thalamocorticals
project to lamina
IV of the cortex.
Corticothalamics
that project back
to the thalamus
originate in lamina
VI of the cortex.
Thalamic Pain Syndrome
Central neurogenic pain (not caused by
activity in peripheral sensory fibers)
can be caused by lesions that interrupt the
somatosensory pathway at any level.
A destructive lesion that involves the ventral
posterior nucleus of the thalamus may result
in the thalamic pain syndrome characterized
by exaggerated and exceptionally disagreeable
responses to cutaneous stimulation.
Cerebral Cortex
There is a complete representation of the body on the
pre- and post-central gyri, called the motor and sensory
homunculus.
The leg is represented on the
medial aspect of the hemisphere
in the paracentral lobule.
Brodmann (1909)
identified about 50
cytoarchitecturally
distinct regions in
the cerebral cortex:
Brodmann’s areas.
These numbers have
become synonymous
with the regions.
From Wilkinson
Associational fibers originate in lamina III pyramidal
cells. Short associational fibers (U-fibers) interconnect
adjacent gyri. Long associational bundles interconnect
distant lobes.
Commissural fibers originate from lamina III pyramidal
cells. There are three major cerebral commissures:
corpus callosum, anterior commissure, and hippocampal
commissure. The corpus callosum interconnects regions
above the superior temporal gyrus. The anterior
commissure interconnects lower temporal regions.
The principal source of cortical afferents is the thalamus.
Corticopetal projectional fibers (thalamocorticals)
traverse the internal capsule to reach the cortex.
Corticofugal
projections
originate from
layer V
pyramidal
neurons,
including
corticospinals,
corticobulbars,
corticopontines,
corticostriates.
Only
corticothalamics
originate in
layer VI.
Associational
Corticostriate
Commissural
Corticopontine
Corticospinal
Corticobulbar
Corticothalamic
Descending projectional fibers traverse the internal
capsule en route to the brainstem. Frontal corticofugals
traverse the anterior limb, while parietal & occipital
corticofugals traverse the posterior limb.
The superior parietal lobule provides essential
information on body image to the premotor cortex.
Lesions of the SPL result in apraxia (inability to perform
learned movements in the absence of paralysis).
The left hemisphere is dominant for language in about
98% of the population. Broca’s motor speech area is in the
inferior frontal gyrus. Wernicke’s area for language
comprehension is in the parieto-occipito-temporal region.
The arcuate fasciculus
(associational fibers) connects
Wernicke’s area to Broca’s area.
Broca’s
Area
Wernicke’s
Area
Aphasias= language dysfunctions
Receptive Aphasias: lesions of Wernicke’s area;
difficulties with language comprehension,
recognition of symbols of language (visual, auditory,
somatosensory)
1. Tactile Agnosias (astereognosis)- supramarginal
gyrus
2. Visual Agnosias (word blindness)- angular gyrus
3. Auditory Agnosias (word deafness)- caudal part
of superior temporal gyrus
Expressive Aphasias: lesions of Broca’s area;
disruption of speech production; poor syntax; word
omissions; normal comprehension of language, but
speech is labored.
When asked to make
drawings, the patient
with a parietal lesion
(unilateral neglect)
draws all the numbers
on a clock face on the
ipsilateral side, or
only draws the
ipsilateral side of the
body in a stick figure.
Attention
Lesion of the
posterior parietal
cortex can
produce
hemi-inattention
syndrome