The document provides an overview of functional neuroanatomy, discussing the triune brain hypothesis which divides the brain into three evolutionary structures: the brainstem (reptilian functions), limbic cortex (emotions and memory), and neocortex (higher functions). It details the anatomical terms used to describe brain locations and structures, focusing on the roles of various brain regions including the thalamus, hypothalamus, and different areas of the cerebral cortex. Additionally, it highlights the importance of interaction among brain systems and the balance necessary for normal functioning, as well as the individual differences in brain anatomy.

1. Functional Neuroanatomy
Vivek Misra |B.Tech, M.S, MIANS
Research Fellow
The Institute of Neurological Sciences
VHS Multi-Specialty Hospital & Research Institute
Chennai. IN
vivek@ubrf.org | @iVivekMisra
http://www.ubrf.org

2. Overview
• A word about the funny names, and
a few definitions
• Anatomy versus Function: The
Triune Brain Hypothesis
• The Brainstem
• The Limbic System
• Cerebral Cortex
Vivek Misra

3. A word about the funny names…
 Early anatomists named most brain structures (in Latin,
for the most part) according to their similarity to
commonplace objects:
 amygdala = almond,
 hippocampus = sea horse,
 genu = knee,
 cortex = bark
 pons = bridge
Vivek Misra

4. A few definitions
Locations in the Brain
 Described relative to neuraxis - an imaginary line drawn
through the spinal cord up to the front of the brain
 The front end is anterior
 The back end is posterior
 The terms rostral (toward the head) and caudal
(toward the tail) are also used when referring to parts
of the brain
Vivek Misra

5. A few definitions
 Dorsal (back) refers to the top of the head and the back
 The ventral (front) surface faces the ground.
 These directions are somewhat more complicated in
humans because our neuraxis bends, so that the top of
the head is now perpendicular to the back.
Vivek Misra

6. The Neuraxis
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Anterior
Posterior
Dorsal
Ventral

7. The Neuraxis
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Anterior
Posterior
Dorsal
Dorsal
Ventral

8. A few definitions
 Lateral means to the side (away from the neuraxis)
 Medial (or mesial) means toward the middle (towards
the neuraxis)
 Proximal: Areas of the brain that are near to one
another
 Distal: Areas that are far from one another
Vivek Misra

9. A few definitions
 Ipsilateral refers to structures on the same side of the
body
 E.g. the olfactory bulbs send ipsilateral connections to
the brain - the right bulb connects to the right
hemisphere, and the left bulb connects to the left
hemisphere
 Contralateral refers to structures on opposite sides of
the body
 E.g. the left motor strip connects to the right side of the
body
Vivek Misra

10. A few definitions
Slices of the brain
 Transversely, like a loaf of bread - also called frontal or
cross sections
 Parallel to the ground, giving us horizontal sections
 Perpendicular to the ground and parallel to the
neuraxis - sagittal section - midsagittal plane divides
the brain in half along the longitudinal fissure
 Because of our upright posture, cross sections of our
spinal cord are actually parallel to the ground
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11. Vivek Misra
Transverse/
Cross section
Horizontal
section
Sagittal
section

12. Gross Anatomy of the Brain
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13. Gross Anatomy of the Brain
• Functional divisions based on evolutionary criteria
Triune Brain Hypothesis (MacLean)
“In its evolution, the forebrain of advanced mammals has
expanded as a triune structure that anatomically and
chemically reflects ancestral commonalities with reptiles,
early mammals, and late mammals.” (1985)
• Mammalian brain structure reflects its phylogeny
Vivek Misra

14. Gross Anatomy of the Brain
The three brains…
1. Reptiles (R-complex) = Brainstem
• Basic regulatory and vegetative functions, “instincts”
2. Early Mammals = Limbic Cortex
• Limbus = border or margin (Latin)
• Explicit memories, emotion
• Care and protection of offspring
• Establishing territory
3. Late Mammals = Neocortex
• Abstract reasoning, long-term planning and behaviour,
higher sensory functioning, etc.
Vivek Misra

15. Is the Triune Brain
Hypothesis Useful?
1. Intuitive, “textbook” way of dividing the structure of the
brain based on its evolutionary usefulness and function
• Most textbooks dealing with brain function use the triune
division
• Accounts how the mammalian brain evolved and became
specialized, beyond basic survival functions common to all
animals
• Accounts for disproportionately large telencephalon
Vivek Misra

16. Is the Triune Brain
Hypothesis Useful?
2. Emphasizes a distributed “systems” approach
• As opposed to a modular approach
• Processing of information proceeds through increasing
levels of complexity
• Multiple brain areas accomplish complex tasks
• Diversity/redundancy of systems (I.e. memory)
• Explains why partial functioning or recovery is possible
Vivek Misra

17. Is the Triune Brain
Hypothesis Useful?
3. Competition between different brain areas
• Conflict between different phylogenic areas of the brain--
situations where different functions come into conflict. (I.e.
smoking)
• Antagonistic or inhibitory areas exist in the brain.
• Mental disease may reflect an imbalance: over- or
underactivity of a brain area
• Role of drug or treatment is to restore balance
Vivek Misra

18. The Brainstem
– Consists of all structures from the thalamus to the
spinal cord
– Regulatory functions: Eating, drinking, body
temperature, sleep and waking, basic movement
and learning
– Generally speaking, these structures rule
functions that are hard-wired, automatic, and not
very plastic
Vivek Misra

19. The Brainstem
Vivek Misra

20. The Brainstem
• Thalamus: A relay centre for sensory information
(touch, vision, hearing); located near the middle of
the cerebral hemispheres.
– Fibres project to primary sensory areas in neocortex
– There are separate nuclei for vision, touch, hearing
– Not a “passive” structure because the majority (80%) of its
connections are not from sensory neurons, but from the
neocortex (including motor areas).
Vivek Misra

21. The Brainstem
• Hypothalamus: Controls all aspects of motivated
(pleasure and pain) and regulatory behaviour
– Autonomic (vegetative) system
– Superior to the pituitary gland, reciprocal connections with
it
– “Master gland”: Closely involved in the regulation and
secretion of hormones
– 0.3% of the brain’s weight
Vivek Misra

22. The Brainstem
• Reticular Formation: Constellation of 90+
nuclei at the base of the brainstem
– Bundles of fibres as well as projections that pass
through to the forebrain from the spinal cord
– A host of regulatory vegetative functions
– connections with cerebral cortex and thalamus
Vivek Misra

23. The Brainstem
• Cerebellum: conspicuous bulbous structure
protruding from the posterior brain; “little
brain”
– Distinctive narrow folds (folia), similar to sulci in
neocortex
– Involved in aspects of learning and coordination of
skilled or smooth movement
– Posture, walking, equilibrium
Vivek Misra

24. The Brainstem
• By and large, there is little that distinguishes
mammals from reptiles in terms of brainstem
structure and function
• An evolutionary turning point occurred with the
specialization of limbic cortex in mammals
• Functions of brainstem aren’t replaced; rather, they
are modified or enhanced by interacting with newer
phylogenic structures.
Vivek Misra

25. The Limbic Cortex
• Three-layer cortical structure covering the
periphery of the brainstem, on the ventral
surface of the lateral ventricles
• Primarily known for its role in emotion,
(emotional) learning and memory
• Also plays a role in spatial learning and
olfaction (memories of odour)
Vivek Misra

26. The Limbic Cortex
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27. The Limbic Cortex
• Hippocampus: Located next to the lateral ventricle in the
temporal lobe.
• Along with the fornix, mammillary bodies, and cingulate gyrus
is involved in learning and memory.
• Amygdala: located anterior to the hippocampus
• only part of the limbic system responsible for emotional
responses
• Other areas involved with learning and memory of emotions
(recognition of emotional events)
Vivek Misra

28. The Limbic Cortex
Fornix: a bundle of axons that connects
hippocampus with other regions of the brain,
including the mammillary bodies (containing some of
the hypothalamic nuclei)
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29. Cerebral Cortex
• Six-layered structure
• Includes most of the two symmetrical cerebral
hemispheres.
• The cerebral hemispheres contain the limbic cortex
 The majority of the surface of the cerebral
hemispheres is called the neocortex
 Part of the cerebral cortex is buried in the frontal
lobes (I.e. insula – taste, sensation, and memory)
Vivek Misra

30. Cerebral Cortex
 In humans the cerebral cortex is very convoluted
 About two-thirds of the brain surface is found in the sulci and
fissures
 The total surface area of the cortex is approximately 2360cm3 ,
3 mm thick
 Sulci - small grooves
 Fissures - large grooves
 Gyri - bulges between sulci or fissures
 Greatly enlarge the surface area of brain
 Provides additional neurons for higher cognitive functions
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31. Vivek Misra

32. Cerebral Cortex
 The cortex is made up mostly of glia (support cells), and
the cell bodies, dendrites, and interconnecting axons of
neurons.
 Neuron cell bodies are grayish brown- that is why the
cortex is called gray matter
 Beneath the cerebral cortex run millions of axons
ensheathed in myelin--white matter--that connects the
neurons of the cerebral cortex with those located
elsewhere
Vivek Misra

33. Cerebral Cortex
Vivek Misra
Significant individual differences in the sulci and gyri.
However, there are major landmarks common to everyone:
The longitudinal fissure divides most of the cortex into left
and right sides.
The central sulcus provides an important dividing line
between the anterior and posterior regions of the cerebral
cortex
Anterior: planning and executing movements
Posterior: sensation, perception and learning

34. Vivek Misra

35. Cerebral Cortex
– Although the two cerebral hemispheres cooperate
with each other, they do not perform identical
functions.
 Some functions are lateralized – located primarily
on one side of the brain
 The left hemisphere is involved in analysis of
information – extraction of elements that make up
a whole
 For instance the left hemisphere is good at
recognizing serial events.
Vivek Misra

36. Cerebral Cortex
 The right hemisphere is specialized for synthesis – putting
isolated elements together to perceive a whole.
 During normal functioning of the brain we are not aware
of lateralization
 Our perceptions and memories are unified by the corpus
callosum – a band of axons that connects the two cerebral
hemispheres
 Connects topographically – i.e. Areas of the brain that are
the same region on both sides
 The corpus callosum is the largest commissure of the brain
– cross-hemispheric connection
Vivek Misra

37. Vivek Misra

38. Cerebral Cortex
• Basal ganglia: A collection of subcortical nuclei in the
forebrain.
 Lie beneath the anterior portion of the lateral ventricles.
 The major parts: caudate nucleus, putamen, and the globus
pallidus.
 These structures are involved in the control of movement
(frontal lobe).
 Parkinson’s disease results from degeneration of the
connections between the midbrain and the caudate nucleus
and putamen.
Vivek Misra

39. Basal Ganglia
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40. Cerebral Cortex
• Its divided into 4 areas, or lobes, named for the bones of the
skull that cover them
 Frontal lobes - includes everything in front of the
central fissure
 Parietal lobe - is located on the side of the cerebral
hemisphere, just behind the central sulcus and caudal
to the frontal lobe
 Temporal lobe - lateral and ventral to the frontal and
parietal lobe
 Occipital lobe - back of the brain - caudal to the parietal
and temporal lobes
Vivek Misra

41. Vivek Misra

42. Cerebral Cortex
Three areas of the cerebral cortex receive contralateral
information from the sensory organs.
 Primary visual cortex - back of the brain on the inner
surfaces of the cerebral hemispheres - upper and lower
parts of the calcarine fissure
 Primary auditory cortex is located on the upper surface
of a deep fissure in the side of the brain - lateral fissure
 Primary somatosensory cortex - vertical strip of cortex
caudal to the central sulcus - receives information from
the body senses primarily touch, pressure, pain
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44. Cerebral Cortex
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45. Cerebral Cortex
 Primary motor cortex - just anterior to the central
sulcus and the primary somatosensory cortex
 most directly involved in the control of movement
 neurons in different parts of the motor cortex are
connected to different muscles in the body
(homunculus)
 connections to muscles are contralateral
Vivek Misra

46. Cerebral Cortex
 The primary parts of the cortex take up a small
proportion of the cortex
 The rest of the cortex is made up of association areas.
Vivek Misra

47. Cerebral Cortex
• Each primary sensory area of the cerebral cortex sends
information to the adjacent regions - sensory association
cortex
 Usually posterior
 Circuits of the neurons in these areas analyze the
information received from the primary sensory cortex
 Perception takes place there and memories are stored
there
Vivek Misra

48. Cerebral Cortex
 The regions of the sensory association cortex located closest to
the primary cortices receive information from only one sensory
system
 E.g. region closest to primary visual cortex is involved in visual
perception and stores visual memories
 Regions further away from the primary cortices integrate
information multiple sensory systems - involved in several kinds
of perception and memories
 Combining vision and hearing to recognize a face or to
understand language
Vivek Misra

49. Cerebral Cortex
• The frontal association cortex is involved in the planning and
execution of movements
 The motor association cortex is located directly rostral
to the primary motor cortex
 This region controls the primary motor cortex - direct
control over behaviour
 The rest of the frontal lobe, rostral to the motor
association cortex is known as the prefrontal cortex -
formulation of plans and strategies
Vivek Misra

50. Summary
1. Divisions of the brain based on structure and
function may be different.
2. Normal brain functioning requires the interaction
of many (inhibitory) systems.
3. Normal brain functioning requires a balance
between all “three” brains.
4. If not, there is disease and dysfunction.
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52. Vivek Misra
fornix

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Basal ganglia

54. The Limbic Cortex
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Hippocampus