3' Diencephalon

1
3. Diencephalon

• The diencephalon may be divided into four strata
  the subthalamus (light tan), the epithalamus
  (dark tan), the thalamus (red), and the
  hypothalamus (green).

2
Subthalamus

• The subthalamus is a continuation of the anterior
  midbrain.
• It is located inferior to the thalamus, lateral
  to the hypothalamus, and anterior to the
  epithalamus.

3
Subthalamus

• It contains nuclei of the extrapyramidal motor
  system and may be regarded as the motor zone of
  the diencephalon.
• It is believed to by the bodys pacemaker and has
  been implicated in Parkinsons disease.
• Deep brain stimulation of the subthalamus is so
  dramatic in reversing the symptoms of PD that it
  has altered the thinking on Parkinsons disease.

4
Subthalamus

• Surgical destruction or stimulation of the
  subthalamus with deep brain stimulation has led
  to the disappearance of the involuntary, writhing
  movements (dyskinesias) that result from
  prolonged and excessive levodopa use.
• Deep brain stimulation of the subthalamus has
  been found to reverse the slowness and poverty of
  movement of PD.

5
Subthalamus

• It is now believed that PD may begin in the
  subthalamus and not the substantia nigra
• In those without PD, damage to the subthalamic
  nucleus produces involuntary movements which may
  increase during seizures to violent of the arms
  or of the entire contralateral side of the body,
  a disorder known as hemiballismus.

6
Epithalamus

• The epithalamus, posterior to the subthalamus,
  contains the pineal gland (epiphysis) and the
  habenular nuclei.
• The pineal gland is an endocrine gland shaped
  like a pine cone and attached to the roof of the
  third ventricle.

7
Eipthalamus

• The gland consists of masses of glial cells and
  secretory cells called pinealocytes.
• The pinealocytes synthesize the hormone melatonin
  and secrete it directly into the cerebrospinal
  fluid, which takes it into the blood.
• Melatonin affects reproductive development and
  daily physiologic cycles.
• Synthesis and release of melatonin is stimulated
  by darkness and inhibited by light.

8
Eipthalamus

• Even without visual cues, the level of melatonin
  in the blood rises and falls on a daily
  (circadian) cycle with peak levels occurring in
  the wee hours of the morning.
• Because the pineal gland lies near the center of
  the brain, it obtains information about light in
  the environment through nerve pathways
  originating in the eyes.
• In general, light slows and darkness stimulates
  the pineal gland's production of melatonin.

9
Eipthalamus

• Therefore, the gland tends to secrete small
  amounts of melatonin during the day and larger
  amounts at night.
• In human beings, melatonin has been linked to the
  onset of puberty.
• Studies have shown that the pineal gland's
  nightly secretion of melatonin decreases when a
  boy or girl reaches puberty.

10
Epithalamus

• Other studies have indicated that melatonin may
  help regulate menstrual cycles in women and sperm
  production in men.
• In addition, researchers have suggested a
  connection between melatonin levels and certain
  mental illnesses and changes in metabolism and
  body adiposity in middle age.

11
Thalamus

•  The thalamus is an oval structure found above
  the midbrain that measures about an inch in
  length.
• It constitutes about 4/5 of the diencephalon.

12
Thalamus

•  Each thalamus consists of two masses of grey
  matter organized into nuclei.
• The white matter portions of the thalamic masses
  divide the grey matter into different nuclear
  groups.

13
Thalamus

• The two thalami are connected to each other by a
  bridge of grey matter that crosses the third
  ventricle.
• It is called the intermediate mass.

14
Thalamus

• Each group of nuclei assumes a particular relay
  role.
• The medial geniculate bodies (dark purple) are
  the relay stations for auditory stimuli coming
  into the CNS.

15
Thalamus

• The lateral geniculate bodies (green) are the
  relay stations for visual stimuli coming into the
  CNS.

16
Thalamus

• The ventral posterior nuclei (fuchsia) are the
  relay stations for information about general
  sensation and taste coming into the CNS.

17
Thalamus

• The outgoing relays in the thalami are the
  ventral lateral nuclei (tan) for voluntary motor
  actions and ventral anterior nuclei (red) for
  involuntary motor actions and arousal.

18
Hypothalamus

• The hypothalamus forms the lowest layer and floor
  of the diencephalon.
• From it the hypophyseal stalk protrudes.
• The hypothalamus is the highest regulatory center
  for the vegetative nervous system.

19
Hypothalamus

• It influences all processes important for the
  maintenance of homeostasis and regulates the
  functions of the organs responding to momentary
  bodily stress warmth, water and electrolyte
  balance, cardiac function, circulation and
  respiration, metabolism, and the sleeping/waking
  rhythm.
• Eating, defecation, gastrointestinal activity,
  fluid intake, urination, procreation, and
  sexuality are regulated from this region.

20
Hypothalamus

• Affective components of pleasure, displeasure,
  happiness, fear, or anger can be aroused through
  hypothalamic stimulation.
• The hypothalamus is divided into major regions
  containing several nuclei.
• The infundibulum, contains neurons that transport
  regulating hormones to the blood vessels and then
  into the anterior lobe of the pituitary gland.

21
Hypothalamus

• Oxytocin and vasopressin are two closely related
  hormones made largely in the hypothalamus which
  are transported by neuronal fibers in the
  infundibulum to the posterior lobe of the
  pituitary gland.

22
Hypothalamus

• Vasopressin regulates the body's retention of
  water.
• It is released when the body is dehydrated and
  causes the kidneys to conserve water, thus
  concentrating the urine, and reducing urine
  volume.
• It also raises blood pressure by inducing
  moderate vasoconstriction.
• Vasopressin is also natures cocktail for male
  attachment and paternal instincts.

23
Hypothalamus

• Like vasopressin, oxytocin is made in the
  hypothalamus as well as in the ovaries and
  testes.
• Unlike vasopressin, oxytocin is released in all
  female mammals, including women, during the
  birthing process.
• It initiates contractions of the uterus and
  stimulates the mammary glands to produce milk.
• Oxytocin also stimulates bonding between a mother
  and her infant.

24
Hypothalamus

• It is now believed that oxytocin is also involved
  in the feelings of adult-male-female attachment.
• In fact, vasopressin and oxytocin are often
  referred to as the two satisfaction hormones.
• They are secreted during sexual intercourse
  during stimulation of the genitals and/or nipples
  and during orgasm.

25
Hypothalamus

• At orgasm, levels of vasopressin dramatically
  increase in men and levels of oxytocin rise in
  women.
• These cuddle chemicals are thought to
  contribute to that sense of fusion, closeness,
  and attachment you feel after sweet sex with a
  beloved (Fisher, 2004).

26
Hypothalamus

• The mammillary region consists of the two small
  mammillary bodies and serve as relay stations for
  olfactory neurons involved in reflexes related to
  the sense of smell.

27
Hypothalamus

• Afferent projections from the external special
  sense organs as well as from internal autonomic
  visceral receptors keep the thalamus apprised of
  changes occurring in both external and internal
  environments.
• Continual monitoring of internal and external
  events allows the hypothalamus to make changes in
  vegetative functions.

28
6. Cerebral Hemispheres

•  The cerebrum is supported on the brainstem and
  forms the bulk of the brain.
• Its surface, referred to as the cerebral cortex,
  is composed of grey matter 2-4 mm thick.

29
Cortex

•  The term cortex (p. cortices) refers to a layer
  or sheet of nervous tissue made up of neuronal
  cell bodies.
• In most areas of the cortex, there are six layers
  of nerve cell bodies.

30
White Matter

• Beneath the cortex (stained purple) lies the
  cerebral white matter.
• Nuclei and cortices are interconnected by the
  axons of projection neurons which are the white
  matter (tracts) of the CNS.

31
Convolutions and Fissures

• During embryonic development, there is a rapid
  increase in brain size.
• The grey matter of the cortex enlarges out of
  proportion to the underlying white matter,
  causing it to roll and fold in upon itself.

32
Convolutions and Fissues

• The folds are called gyri (s. gyrus) if they are
  small or convolutions if there are big.
• Fissures are deep grooves between the folds,
  whereas sulci (s. sulcus) are shallow grooves
  between the folds.

33
Cerebral Landmarks

• Renaissance anatomists found that the most
  prominent infoldings were invariant from one
  human brain to the next, so they used these
  features as landmarks to separate the brain into
  distinct regions.

34
Median Longitudinal Fissure

• The most prominent landmark of the cerebrum is
  median longitudinal fissure.
• It separates the cerebrum along the midline into
  two fairly symmetrical halves.

35
Cerebral Hemispheres

• These two halves are referred to as the cerebral
  hemispheres.
• They are connected internally by a large bundle
  of transverse white matter fibers called the
  corpus callosum.

36
Cerebral Lobes

• Each hemisphere can be divided further into four
  lobes, named for the overlying bones of the
  skull the frontal lobe, the temporal lobe, the
  parietal lobe, and the occipital lobe.

37
Central Sulcus

• A cleft called the central sulcus (aka Rolandic
  fissure) separates the cerebral hemisphere into
  anterior and posterior portion.

38
Frontal and Parietal Lobes

• The anterior portion is known as the frontal lobe
  (pink) the posterior portion as the parietal lobe
  (blue).

39
Landmark Gyri

•  Within each one of these lobes are important
  gyri, that also serve as landmarks for important
  processing regions of the lobes.

40
Precentral Gyrus

•  Immediately anterior to the central sulcus is
  the precentral gyrus, the primary motor area (M1)
  of the cerebral cortex of the frontal lobe.

41
Post Central Gyrus

•  Immediately posterior to the central sulcus is
  the postcentral gyrus, the primary sensory area
  (S1) of the cerebral cortex of the parietal lobe.

42
Parietal Gyri

• Within the parietal lobe are two other prominent
  gyri.
• Curving above the end of the lateral sulcus is
  the supramarginal gyrus (SmG).
• Curving off the end of the lateral sulcus is the
  angular gyrus (AnG).

43
Parietal Gyri

• Both of these gyri, because of their location,
  where sensory, auditory, and visual information
  come together, have important roles in
  multi-modal processing tasks, such as reading,
  writing, arithmetic, and construction.

44
Lateral Sulcus

•  Another consistent cleft within each cerebral
  hemisphere divides the hemisphere into upper and
  lower portion.
• This cleft is termed the lateral sulcus (aka
  Sylvian Fissure).

45
Temporal Lobe

•  The temporal lobe lies beneath the lateral
  sulcus.

46
Heschls Gyrus

•  Heschls gyrus is located on the superior
  temporal gyrus, and extends into the lateral
  sulcus.
• It is the site of the primary auditory area (A1).

47
Occipital Lobe

•  On the lateral surface of the cerebral
  hemisphere, there is no clear landmark
  demarcating the occipital lobe.
• However, it is the most posterior lobe that can
  be visualized on the lateral surface of the
  cerebrum.

48
Occipital Pole

•  The primary visual area (V1) covers the entire
  occipital pole.

49
Calcarine Fissure

•  On the mesial surface of the hemisphere,
  however, the primary visual cortex is visible on
  the banks of the calcarine fissure.

50
Insula

•  An additional area of the cerebral cortex became
  buried in the depths of the lateral sulcus during
  development of the telecephalon.
•  This cortex, called the insula, can be revealed
  by prying open the lateral sulcus.

51
Opercular Covering

•  The portions of the frontal (5), parietal (6),
  and temporal (7) cortices that cover the insula
  are referred to as the operculum.
•  The insula as well as the frontal-parietal
  operculum constitute the gustatory (taste) cortex.

52
White Matter

•  The white matter underlying the cortex consists
  of myelinated axons running in three principle
  directions.

53
Association Fibers

•  Association fibers connect and transmit nerve
  impulses between gyri in the same hemisphere.

54
Association Fibers

•  The arcuate fasciculus is an important bundle of
  association fibers that links the temporal lobe
  with the frontal lobe, through the parietal lobe.
• It has been implicated in some of the expressive
  output difficulties of individuals with aphasia.

55
Commissural Fibers

•  Commissural fibers transmit impulses from the
  gyri in one hemisphere to the corresponding gyri
  in the opposite cerebral hemisphere.
• Examples of commissural fibers include the corpus
  callosum, the anterior commissure, and the
  posterior commissure.

56
Corpus Callosum

•  The corpus callosum consists of cables of tissue
  that connect the two hemispheres.
• It is composed of some two hundred million fibers
  that link the two brain halves from the forehead
  to the back of the head.

57
Anterior Commissure

• At least one section of the corpus callosum is
  somewhat thicker in women than in men.
• The anterior commissure is the second tissue
  bridge connecting brain hemispheres.
• It is 12 larger in women than in men.

58
Anterior Commissure

• These thicker connections are believed to allow
  for greater communication between the two brain
  hemispheres.
• In males, the two brain halves are less in touch
  each side operates more independently.
• Because the male brain is more lateralized, with
  each hemisphere more rigidly dedicated to doing
  one task or another, this set up may enable men
  to focus their attention more intensely than
  women.

59
Anterior Commissure

• Womens well-connected brains may facilitate
  their ability to gather, integrate, and analyze
  more diverse kinds of informationan aspect of
  web thinking.
• Womens less lateralized, more left/right
  integrated brain probably helps then to embrace
  the larger view.
• They dont see things as cut and dried, the way
  that men do (Schultz, cited in Fisher, 1999).

60
Projection Fibers

•  Projection fibers form ascending and descending
  tracts that transmit impulses from the cerebrum
  to other parts of the brain and spinal cord.
• These diffuse tracts form the corona radiata (1).

61
Basal Ganglia

•  The basal ganglia consist of several large
  subcortical masses of grey matter (nuclei) buried
  deep within the subcortical white matter.
• They include the caudate nucleus and the
  lenticular (lentiform) nucleus.

62
Caudate Nucleus

•  The caudate nucleus is a C-shaped structure with
  an anteriorly located head deep in the frontal
  lobe.
• Its body stretches in a superior and posterior
  direction following the lateral ventricle around.

63
Caudate Nucleus

• Its inferiorly directed tail ends in the temporal
  lobe, with the amygdala attached.
• The lenticular nucleus is comprised of the
  putamen and globus pallidus.

64
Lenticular Nucleus

• The lenticular nucleus is separated from the
  caudate nucleus by the internal capsule.
• The internal capsule is a compact bundle of
  fibers through which most of the neural traffic
  to and from the cortex passes.

65
Basal Ganglia

• The caudate and putamen receive most of their
  input from the cerebral cortex.
• In this sense they are the doorway into the
  basal ganglia.
• The medial caudate receives its input from
  frontal cortex and limbic areas, and is
  implicated more in thinking and schizophrenia
  than in moving and motion disorders.

66
Basal Ganglia

• Indeed, the body and tail of the caudate become
  particularly active in the brains reward
  systemthe minds network for general arousal,
  sensations of pleasure, and the motivation to
  acquire rewards.
• The caudate helps us detect and perceive a
  reward, discriminate between rewards, prefer a
  particular reward, anticipate a reward, and
  expect a reward.

67
Basal Ganglia

• It produces motivation to acquire a reward and
  plans specific movements to obtain a reward.
• We will talk about the motivation and reward
  system in romantic love when we explore the
  reticular networks!
• The caudate is also associated with the acts of
  paying attention and learning.

68
6. Cerebral Hemispheres

• The caudate and putamen are reciprocally
  interconnected with the substantia nigra, but
  send most of their output to the globus pallidus

69
Basal Ganglia

• Although there are many different
  neurotransmitters used within the basal ganglia
  the overall effect of the basal ganglia on
  thalamus is inhibitory.
• The function of the basal ganglia is often
  described in terms of a "brake hypothesis.
• To sit still, you must put the brakes on all
  movements except those reflexes that maintain an
  upright posture.

70
Brake Hypothesis

• To move, you must apply a brake to some postural
  reflexes, and release the brake on voluntary
  movement.
• In such a complicated system, it is apparent that
  small disturbances can throw the whole system out
  of whack, often in unpredictable ways.
• The deficits resulting from damage or malfunction
  of the basal ganglia tend to fall into one of two
  categories the presence of extraneous unwanted
  movements or an absence or difficulty with
  intended movements.

71
Basal Ganglia Defects

• Huntington's disease, or chorea, is a hereditary
  disease of unwanted movements.
• It results from degeneration of the caudate and
  putamen, and produces continuous dance-like
  movements of the face and limbs.

72
7. The Limbic System

•  If you look at the mesial surfaces of the
  hemispheres, you see an arch-like pattern of
  cortex surrounding the non-convoluted central
  portions of the brain.

73
Limbic Gyri

• The cortical gyri that form a ring around the
  diencephalon include the subcallosal gyrus, the
  cingulate gyrus, and the parahippocampal gyrus.
• Broca referred to this ring of cortex as the
  limbic lobe.

74
Limbic Structures

• Much later, Papez (1937) proposed that limbic
  circuits were the basis of emotion.
• He hypothesized that emotion was not a function
  of any specific brain center but of a circuit
  that interconnected four basic structures the
  hypothalamus with its mammillary bodies, the
  anterior thalamic nucleus, the cingulate gyrus,
  and the hippocampus.

75
The Limbic System

• More recently, Paul MacLean, accepting the
  essential bases of the Papez proposal, created
  the denomination limbic system and added new
  structures to the circuit the orbitofrontal and
  medial frontal cortices (prefrontal area), the
  parahippocampal gyrus, the amygdala, the medial
  thalamic nucleus, and the septal area.

76
Limbic Operations

• Limbic operations tend to fall into the
  emotional-affective realm.
• In short, the limbic system is responsible for
  seven functionsthe four Msmating, mood,
  motivation, and memory and the three Fs--
  fear, fighting, food.
• The septal region is thought to be involved in
  feeling and expressive states conducive to
  sociability and the procreation of the species.

77
The Septal Region

• Parts of the septum are associated with the
  processing of and registering of emotion.
• Individual functions within the region have been
  difficult to tease apart, because of the many
  interconnections with other limbic and brainstem
  regions.

78
The Cingulate Gyrus

• The cingulate gyrus also connects many key sites.
• In this region, emotions, attention, and working
  memory interact.
• It is thought to help us to personally animate
  our attention and to attach it to things in
  external space.

79
The Cingulate Gyrus

• Some parts are associated with happy states.
• Others involve awareness of ones own emotional
  state and the ability to assess other peoples
  feelings during social interactions.

80
The Cingulate Gyrus

• Some other areas are associated with split-second
  emotional reactions to a win or loss, thereby
  judging a reward's value.
• Damage to an area of the cingulate gyrus could
  affect outflow throughout the network, affecting
  the way a person melds affect and higher
  functions.
• The result could be the emotional devaluation or
  depersonalization of events taking place in the
  opposite half of space.

81
The Amygdala

• The amygdala or little almond lies buried deep
  within the antero-inferior region of the temporal
  lobe.
• It has connections to the hippocampus, the septal
  nuclei, the prefrontal area and the medial dorsal
  nucleus of the thalamus.

82
The Amygdala

• These connections make it possible for the
  amygdala to play an important role in the
  mediation and control of major affective
  activities like friendship, love and affection,
  on the expression of mood and, on fear, rage and
  aggression.
• The amygdala, being the center for identification
  of danger, is fundamental for self preservation.

83
The Amygdala

• If you remember only one word about the amygdala,
  the word is FEAR.
• The amygdala is the nucleus responsible for the
  lurch you feel in your stomach when you turn
  around in a dark alley and notice someone
  following you.
• It couples a learned sensory stimulus (man in ski
  mask in alley danger) to an adaptive response
  (fight or flight).

84
The Amygdala

• The amygdala must get sensory input, and fairly
  highly processed input, to recognize the elements
  of a scene that signal danger.
• The association areas of visual, auditory, and
  somatosensory cortices are the main inputs to the
  amygdala.
• The main outputs of the amygdala are to the
  hypothalamus and brainstem autonomic centers,
  including the vagal nuclei and the sympathetic
  neurons.

85
The Amygdala

• The amygdala are thought to have a role in
  controlling the autonomic system to provoke such
  an instant sympathetic response.
• When triggered, it gives rise to fear and anxiety
  which leads to a stage of alertness, getting
  ready to flight or fight.
• Experimental destruction of both amygdala in
  animals makes them tame and sexually
  non-discriminative, and indifferent to danger.

86
The Amygdala

• The electrical stimulus of these structures
  elicits crises of violent aggressivety.
• Humans with marked lesions of the amygdala, lose
  the affective meaning of the perception of
  outside information, like the sight of a well
  known person.
• The subject knows exactly who the person is, but
  is not capable to decide whether he likes or
  dislikes him (or her).

87
The Hippocampus

• If the amygdala is FEAR, then the hippocampus is
  MEMORY.
• The hippocampus is particularly involved with
  memory phenomena, specially with the formation of
  long-term memory.

88
The Hippocampus

• There are at least three different types of
  memory.
• The most short term is working memory.
• Working memory is like the RAM of a computer.
• It is the type of memory that enables you to spit
  back the last sentence of a conversation when
  someone accuses you of not listening.

89
The Hippocampus

• Like the RAM of a computer, it is crucial for
  performing some common operations in your head
  adding numbers, composing a sentence, following
  directions, etc.
• Also like a computer, the space devoted to that
  operation is recycled as soon as you turn to
  something else.
• It does not become a permanent memory.

90
The Hippocampus

• Working memory does not require the
  hippocampus--it is probably a cortical
  phenomenon.
• The second type of memory long-term or
  declarative memory.
• It is composed of all the facts, figures, and
  names you have ever learned.
• All of your experiences and conscious memory fall
  into this category.

91
The Hippocampus

• It is analogous to the hard drive of a computer.
• Although no one knows exactly where this enormous
  database is stored, it is clear that the
  hippocampus is necessary to file away new
  memories as they occur.
• The third type of memory is procedural memory.
• It is probably the most durable form of memory.

92
The Hippocampus

• Procedural memory contains actions, habits, or
  skills that are learned simply by repetition.
• Examples include playing tennis, playing an
  instrument, solving a puzzle, etc.
• The hippocampus is not involved in procedural
  memory, but it is likely that the cerebellum
  plays a role in some instances.

93
The Hippocampus

• The significance of the hippocampus is driven
  home by a famous patient named H.M.
• As part of an epilepsy surgery, doctors removed
  most of his medial temporal lobes.
• Since that surgery, in 1953, he has formed no new
  memories.
• He can remember his childhood and everything
  before the surgery, and he still has working
  memory and the ability to form procedural
  memories.

94
The Hippocampus

• You can have a normal, lucid conversation with
  him, but if you leave the room for a moment, when
  you return he will not remember you or the
  conversation.
• He has completely lost the ability to lay down
  declarative memory.
• Therefore, the hippocampus is critical in laying
  down declarative memory, but is not necessary for
  working memory, procedural memory, or memory
  storage.

95
The Hippocampus

• Damage to the hippocampus will only affect the
  formation of new declarative memories.
• In the case of Alzheimers disease, the slow
  destruction of the hippocampus results in
  problems with consolidating new memories.
• The subject quickly forgets any recently received
  message, in spite of retained long-term and
  procedural memory ability.

96
The Limbic System

• To summarize, then, the limbic system, with its
  interconnectivity to the cortex, diencephalon,
  and midbrain, functions to set the emotional tone
  of the mind.
• It filters external events through internal
  states (emotional coloring) and tags events as
  internally important.
• It stores highly charged emotional memories,
  modulates motivation, and promotes bonding.

97
The Limbic System

• As it directly processes the sense of smell, it
  has a role in hunger drive and modulating libido.
• When the limbic circuit is damaged, moodiness,
  irritability, clinical depression may be seen.
• There is increased negative thinking, a flood of
  negative emotions, and perception of events in a
  negative way.
• Accompanying decreased motivation, there may be
  appetite and sleep problems and decreased or
  increased sexual responsiveness