Sections of the brain

• The front end is the rostral end, meaning

“nose”
• The opposite end is the caudal end, the “tail”
• Along his back is the dorsal surface
• The bottom surface along the dog’s belly is
the ventral surface.
• We can refer to the dog’s nervous system
by using the same coordinates.
• The part of the brain toward the front is the
rostral end (toward the frontal lobes);
• The posterior end is the caudal end (toward the
occipital lobe).
• Along the top of his head is the dorsal surface,
and the bottom surface of the brain is the
ventral surface.
• In humans, we also use the terms superior and
inferior to refer to the top and bottom of the
brain, respectively.
• Similarly, along with the terms rostral, which
still means “toward the frontal pole,” and
• caudal, which still means “toward the occipital
pole,”
• anterior and posterior are also used to refer to
the front and back of the brain, respectively.
• When we consider the spinal cord, the
coordinate systems align with the body axis.
Thus, in the spinal cord, rostral means “toward
the brain,”
 Brain Slices
• Brain slices usually will be in one of three planes.
• If we slice it from nose to tail, that is a sagittal
section.
• When that slice is directly through the middle, it
is a midsagittal or medial section.
• If it is off to the side, it is a lateral section (single
portion)
• If sliced from top to bottom, separating the front
of the brain from the back, we have made a
coronal section.
• If we slice in a plane that separates dorsal
from ventral, that is known as either an axial,
transverse, or horizontal section.
 The Chambers of the Brain
• Scientists have understood for many decades that
neurons in the brain are functional units, and that
how they are interconnected yields specific circuits
for the support of particular behaviors.
• Centuries ago, early anatomists, believing that the
head contained the seat of behavior, examined the
brain to see where the conscious self (soul, if you
wish) was located.
• They found a likely candidate: Some chambers in the
brain seemed to be empty (except for some fluid) and
thus were possible containers for higher functions.
These chambers are called ventricles
 CSF is produced continuously by
Choroid Plexuses – Network of
capillaries that protrude into the
ventricles from the pia mater lining

The excessive CSF is absorbed from

CSF Subarachnoid space into the large
blood-filled spaces

Hydrocephalus
 Function of chambers within the brain
• The brain weighs a considerable amount but has
little or no structural support; there is no skeletal
system for the brain.
• To overcome this potential difficulty, the brain is
immersed in a fluid called cerebrospinal fluid
(CSF).
• This fluid allows the brain to float to help offset
the pressure that would be present if the brain
were merely sitting on the base of the skull.
• This fluid allows the brain to float to help offset
the pressure that would be present if the brain
were merely sitting on the base of the skull.
• CSF also reduces shock to the brain and spinal
cord during rapid accelerations or decelerations,
such as when we fall or are struck on the head.
• The ventricles inside the brain are continuous
with the CSF surrounding the brain.
• The largest of these chambers are the lateral
ventricles, which are connected to the third
ventricle in the brain’s midline.
• The cerebral aqueduct joins the third to the
fourth ventricle in the brainstem below the
cerebellum.
• The CSF is produced in the lateral ventricles and
in the third ventricle by the choroid plexus, an
out pouching of blood vessels from the
ventricular wall.
• Hence, CSF is similar to blood, being formed
from an ultrafiltrate of blood plasma; essentially,
CSF is a clear fluid containing proteins, glucose,
and ions, especially potassium, sodium, and
chloride.
• It slowly circulates from the lateral and third
ventricles through the cerebral aqueduct to the
fourth ventricle and on to the subarachnoid
space surrounding the brain,
• To be reabsorbed by the arachnoid villi in the
sagittal sinus between both the hemispheres on
the dorsal surface.
 Gray Matter
• The more centrally located gray matter, consisting
of neuronal bodies, resembles a butterfly with
two separate sections or horns: the dorsal horn
and ventral horn .
• The ventral horn contains the large motor
neurons that project to muscles.
• The dorsal horn contains sensory neurons and
interneurons.
• The interneurons project to motor neurons on
the same (ipsilateral ) and
• opposite (contralateral ) sides of the spinal cord
to aid in the coordination of limb movements.
• The gray matter surrounds the central canal ,
which is an anatomical extension of the
ventricles in the brain and contains
cerebrospinal fluid.
 The Brainstem: Medulla, Pons,
Cerebellum, and Midbrain

• Brainstem as having three main parts:

the medulla (myelencephalon),
• the pons and cerebellum (metencephalon),
and the midbrain (mesencephalon).
• These three sections form the central nervous
system between the spinal cord and the
diencephalon.
• Though the brainstem is rather small compared to
the vast bulk of the forebrain it plays a starring role in
the brain.
• It contains groups of motor and sensory nuclei, nuclei
of widespread modulatory neurotransmitter systems,
• and white matter tracts of ascending sensory
information and descending motor signals.
• Damage to the brainstem is life threatening, largely
because brainstem nuclei control respiration and
global states of consciousness such as sleep and
wakefulness.
• The medulla, pons, and cerebellum make up the
hindbrain
 Medulla
• The brainstem’s most caudal portion is the
medulla, which is continuous with the spinal
cord.
• The medulla is essential for life. It houses the
cell bodies of many of the 12 cranial nerves,
• providing sensory and motor innervations to the
face, neck, abdomen, and throat (including
taste) as well as the motor nuclei that innervate
the heart.
• The medulla controls vital functions such as
respiration, heart rate, and arousal.
• All of the ascending somatosensory information
entering from the spinal cord passes through the
medulla via two bilateral nuclear groups, the
gracile and cuneate nuclei.
• These projection systems continue through the
brainstem to synapse in the thalamus en route
to the somatosensory cortex.
• Another interesting feature of the medulla is
that the corticospinal motor axons, tightly
packed in a pyramid-shaped bundle (called the
pyramidal tract )
• Thus, the motor neurons originating in the right
hemisphere cross to control muscles on the left
side of the body, and vice versa.
• Functionally, the medulla is a relay station for
sensory and motor information between the
body and brain; it is the crossroads for most of
the body’s motor fibers;
• It controls several autonomic functions,
including the essential reflexes that determine
respiration, heart rate, blood pressure, and
digestive and vomiting responses.
 Pons
• The pons , Latin for “bridge,” is so named because it
is the main connection between the brain and the
cerebellum.
• Sitting anterior to the medulla, the pons is made up
of a vast system of fiber tracts interspersed with
nuclei
• Many of the cranial nerves synapse in the pons;
these include the sensory and motor nuclei from
the face and mouth and the visuomotor nuclei
controlling some of the extraocular muscles.
• Thus, the pons is important for some eye
movements as well as those of the face and mouth.
• In addition, some auditory information is
channeled through another pontine structure,
the superior olive.
• This level of the brainstem contains a large
portion of the reticular formation that
modulates arousal.
• Interestingly, the pons is also responsible for
generating rapid eye movement (REM) sleep.
 Cerebellum
• The cerebellum (literally, “small cerebrum” or
“little brain”), which clings to the brainstem at
the level of the pons, is home to most of the
brain’s neurons.
• Visually, the surface of the cerebellum appears to
be covered with thinly spaced, parallel grooves;
but in reality , it is a continuous layer of tightly
folded neural tissue (like an accordion).
• It forms the roof of the fourth ventricle and sits
on the cerebellar peduncles (meaning “feet”),
which are massive input and output fiber tracts of
the cerebellum.
• The cerebellum has several gross subdivisions,
including the cerebellar cortex, four pairs of deep
nuclei, and the internal white matter. In this way,
the cerebellum resembles the forebrain’s cerebral
hemispheres.
• Most of the fibers arriving at the cerebellum
project to the cerebellar cortex, conveying
information about motor outputs and sensory
inputs describing body position.
• Inputs from vestibular projections involved in
balance, as well as auditory and visual inputs,
also project to the cerebellum from the
brainstem.
• The output from the cerebellum originates in
the deep nuclei.
• Ascending outputs travel to the thalamus and
then to the motor and premotor cortex.
• Other outputs project to nuclei of the
brainstem, where they impinge on descending
projections to the spinal cord.
• The cerebellum is critical for maintaining
posture, walking, and performing coordinated
movements.
• It does not directly control movements; instead,
it integrates information about the body, such as
its size and speed, with motor commands.
• Then, it modifies motor outflow to effect
smooth, coordinated movements.
• If your cerebellum is damaged, your movements
will be uncoordinated and halting, and you may
not be able to maintain balance.
 Midbrain
• The mesencephalon, or midbrain , lies superior
to the pons and can be seen only in a medial
view.
• It surrounds the cerebral aqueduct, which
connects the third and fourth ventricles.
• Its dorsal portion consists of the tectum
(meaning “roof”), and its ventral portion is the
tegmentum (“covering”)
• Large fiber tracts course through the ventral
regions from the forebrain to the spinal cord,
cerebellum, and other parts of the brainstem.
• The midbrain also contains some of the cranial
nerve ganglia and two other important
structures: the superior and inferior colliculi.
• The superior colliculus plays a role in perceiving
objects in the periphery and orienting our gaze
directly toward them, bringing them into sharper
view.
• The inferior colliculus is used for locating and
orienting toward auditory stimuli.
• Another structure, the red nucleus, is involved in
certain aspects of motor coordination.
• It helps a baby crawl or coordinates the swing
• of your arms as you walk. Much of the
midbrain is occupied by the mesencephalic
reticular formation,
• A rostral continuation of the pontine(relating
to) and medullary reticular formation.
 The Diencephalon: Thalamus and
Hypothalamus
• The diencephalon, which is made up of the
thalamus and hypothalamus .
• These subcortical structures are composed of
groups of nuclei with interconnections to
widespread brain areas.
• Thalamus Almost smack dab in the center of
the brain and perched on top of the brainstem
(at the rostral end)
• The thalamus is the larger of the diencephalon
structures.
• The thalamus is divided into two parts—one in
the right hemisphere and one in the left —that
straddle the third ventricle.
• In most people, the two parts are connected by a
bridge of gray matter called the massa intermedia.
• Above the thalamus are the fornix and corpus
callosum; beside it is the internal capsule ,
containing ascending and descending axons
running between the cerebral cortex and the
medulla and spinal cord.
 Fornix
• The fornix (meaning "arch"
in Latin) is a C-shaped
bundle of nerve fibers in
the brain that acts as the
major output tract of the
hippocampus. The fornix
also carries some afferent
fibers to the hippocampus
from structures in the
diencephalon and basal
forebrain. The fornix is part
of the limbic system.
 Corpus Callosum
• corpus callosum- The corpus callosum is the
white matter tracts that connect the left and
right cerebral hemispheres.
• The thalamus has been referred to as the
“gateway to the cortex” because, except for
some olfactory inputs, all of the sensory
modalities make synaptic relays in the thalamus
before continuing to the primary cortical
sensory receiving areas.
• The thalamus is involved in relaying primary
sensory information. It also receives inputs from
the basal ganglia, cerebellum, neocortex, and
medial temporal lobe and sends projections back
to these structures to create circuits involved in
many different functions.
• It also relays most of the motor information that
is on its way to the spinal cord. Thus, the
thalamus, a veritable Grand Central Station
• of the brain, is considered a relay center where
neurons from one part of the brain synapse on
neurons that travel to another region.
• In the thalamus, information can be reorganized
and shuttled, like in a train station switching yard,
according to the connection patterns formed by
the neurons.
 Hypothalamus
• The main link between the nervous system and the
endocrine system is the hypothalamus, which is
the main site for hormone production and control.
• Easily located, it lies on the floor of the third
ventricle.
• It receives inputs from the limbic system structures
and other brain areas. One of its jobs is to control
circadian rhythms (light–dark cycles) with inputs
from the mesencephalic reticular formation,
amygdala, and the retina.
•
• Extending from the hypothalamus are major
projections to the prefrontal cortex, amygdala,
spinal cord, and pituitary gland. The pituitary
gland is attached to the base of the
hypothalamus.
• The hypothalamus controls the functions
necessary for maintaining the normal state of
the body (homeostasis).
• It sends out signals that drive behavior to
alleviate such feelings as thirst, hunger, and
fatigue, and it controls body temperature and
circadian cycles.
• It accomplishes much of this work through the
endocrine system and via control of the
pituitary gland.
• The hypothalamus produces hormones, as well
as factors that regulate hormone production in
other parts of the brain. For example,
hypothalamic neurons send axonal projections
to the median eminence , an area bordering the
pituitary gland.
• There it releases peptides (releasing factors) into
the circulatory system of the anterior pituitary
gland.
• These in turn trigger (or inhibit) the release of a
variety of hormones from the anterior pituitary into
the bloodstream, such as growth hormone, thyroid-
stimulating hormone, adrenocorticotropic
hormone, and the gonadotropic hormones.
• There they stimulate the gland to release the
hormones vasopressin and oxytocin into the blood
to regulate water retention in the kidneys, milk
production, and uterine contractility, among other
functions.
 The Telencephalon: Limbic
System, Basal Ganglia, and
Cerebral Cortex
• The most highly developed and anterior part of
the forebrain, consisting chiefly of the cerebral
hemispheres.
• The telencephalon develops into the cerebrum,
which includes the cerebral cortex, the limbic
system, and the basal ganglia.
 Limbic System
• The “classical” limbic lobe is made up of the
cingulate gyrus (a band of cerebral cortex that
extends above the corpus callosum in the
anterior–posterior direction and spans both the
frontal and parietal lobes), the hypothalamus,
anterior thalamic nuclei, and the hippocampus,
an area located on the ventromedial aspect of
the temporal lobe.
• The “classical” limbic lobe is made up of the
cingulate gyrus (a band of cerebral cortex that
extends above the corpus callosum in the
anterior–posterior direction and spans both
the frontal and parietal lobes), the
hypothalamus, anterior thalamic nuclei, and
the hippocampus , an area located on the
ventromedial aspect of the temporal lobe.
• In the 1930s James Papez ( pronounced
“payps”) first suggested the idea that these
structures were organized into a system for
emotional behavior, which led to the use of the
term Papez circuit.
• It was named the limbic system by Paul
MacLean in 1952 when he suggested the
addition of more brain areas, such as the
amygdala and prefrontal cortex.
• The classical limbic system, as noted earlier,
has been extended to include the amygdala , a
group of neurons anterior to the
hippocampus, along with the orbitofrontal
cortex and parts of the basal ganglia.
• Sometimes the medial dorsal nucleus of the
thalamus is also included.
Limbic System
 ****Basal Ganglia
• The basal ganglia are a collection of nuclei
bilaterally located deep in the brain beneath the
anterior portion of the lateral ventricles, near
the thalamus.
• These subcortical nuclei, the caudate nucleus,
putamen, globus pallidus, subthalmic nucleus,
and substantia nigra, are extensively
interconnected.
• The caudate nucleus together with the putamen
is known as the striatum.
• The basal ganglia receive inputs from sensory
and motor areas, and the striatum receives
extensive feed back projections from the
thalamus. A comprehensive understanding of
how these deep brain nuclei function remains
elusive.
• They are involved in a variety of crucial brain
functions including action selection, action
gating, motor preparation, timing, fatigue, and
task switching (Cameron et al., 2009).
• Notably, the basal ganglia have many dopamine
receptors. plays a crucial role in motivation and
learning.
• The basal ganglia may also play a big role in
reward-based learning and goal-oriented
behavior.
• One summary of basal ganglia function
proposes that it combines an organism’s
sensory and motor context with reward
information and passes this integrated
information to the motor and prefrontal cortex
for a decision (Chakravarthy et al., 2009).
 The Cerebral Cortex
• The crowning glory of the cerebrum is its
outermost tissue, the cerebral cortex. It is
made up of large sheets of (mostly) layered
neurons, draped and folded over the two
symmetrical hemispheres like frosting on a
cake.
• It sits over the top of the core structures
including parts of the limbic system and basal
ganglia, and surrounds the structures of the
diencephalon.
• The term cortex means “bark,” as in tree bark,
and in higher mammals and humans it
contains many infoldings, or convolutions
• The infoldings of the cortical sheet are called
sulci (the crevices crevices) and gyri (the
crowns of the folded tissue that one observes
when viewing the surface).
• The folds of the human cortex serve several
functions. First, they enable more cortical
surface to be packed into the skull.
• The total surface area of the human cerebral
cortex is about 2,200 to 2,400 cm2, but because
of extensive folding, about two thirds of this
area is confined within the depths of the sulci.
Second, having a highly folded cortex brings
neurons into closer three - dimensional
relationships to one another, reducing axonal
distance and hence neuronal conduction time
between different areas.
• This savings occurs because the axons that make
long-distance corticocortical connections run
under the cortex through the white matter and
do not follow the folding's of the cortical surface
in their paths to distant cortical areas. Third, by
folding, the cortex brings some nearby regions
closer together.
• The cortex ranges from 1.5 to 4.5 mm in
thickness, but in most regions it is approximately
3 mm thick.
• The cortex contains the cell bodies of neurons,
their dendrites, and some of their axons.
• In addition, the cortex includes axons and axon
terminals of neurons projecting to the cortex
from other brain regions, such as the
subcortical thalamus.
• The cortex also contains blood vessels. Because
the cerebral cortex has such a high density of
cell bodies, it appears grayish in relation to
underlying regions that are composed primarily
of the axons that connect the neurons of the
cerebral cortex to other locations in the brain.
 Dividing the Cortex Anatomically
• The cerebral hemispheres have four main
divisions, or lobes, that are best see n in a
lateral view: the frontal, parietal, temporal,
and occipital lobes. observed first in the
graying of hair.
• The word temporal derives from Latin
“tempora,” meaning “time.”
• The occipital lobe is demarcated from the
parietal and temporal lobes by the parieto-
occipital sulcus on the brain’s dorsal surface
and the preoccipital notch located on the
ventrolateral surface.
• The left and right cerebral hemispheres are
separated by the interhemis pheric fissure
(also called the longitudinal fissure; that runs
from the rostral to the caudal end of the
forebrain.
• Hidden from the lateral surface view are other
parts of the cerebrum, not all of which are
conveniently
• contained in the four lobes. For instance, the
insula is located between the temporal and
frontal lobe, and is, as its name implies, an
island of folded cortex hidden deep in the
lateral sulcus.
• The insula, which is surprisingly large, is divided
into the larger anterior insula and smaller
posterior insula.
 Dividing the Cortex
Cytoarchitectonically
• The cerebral cortex can be more finely divided,
both anatomically and functionally. We will take
a look at both.
• Cytoarchitectonics uses the microanatomy of
cells and their organization to subdivide the
cortex ( cyto– means “cell” and architectonics
means “ architecture”).
• Using histological analysis, tissue regions are
defined in which the cellular architecture looks
similar, and therefore might indicate areas of
homogeneous function.
• This work began in earnest with Korbinian
Brodmann at the beginning of the 20th century
• Brodmann identified approximately 52 regions of
the cerebral cortex.
• These areas were categorized and numbered
according to differences in cellular morphology
and organization.
• Other anatomists further subdivided the
cortex into almost 200 cytoarchitectonically
defined areas.
• A combination of cytoarchitectonic and
functional descriptions of the cortex is
probably the most effective way of dividing
the cerebral cortex into meaningful units.
• The Brodmann system often seems unsystematic.
Indeed, the numbering has more to do with the
order in which Brodmann sampled a region than
with any meaningful relation between areas.
• Nonetheless, in some regions the numbering
system roughly corresponds with the relations
between areas that carry out similar functions,
such as vision—e.g., Brodmann areas 17, 18, and
19.
• Unfortunately, the nomenclature of the cortex
(and indeed the nervous system) is not fully
standardized.
• Ninety percent of cortex is composed of
Neocortex: cortex that contains six cortical layers
or that passed through a developmental stage
involving six cortical layers.
Neocortex includes areas like primary sensory
and motor cortex and association cortex (areas
not obviously primary sensory or motor).
• Mesocortex is a term for the so-called
paralimbic region, which includes the cingulate
gyrus, parahippocampal gyrus, insular cortex,
and orbitofrontal cortex.
• Mesocortex is interposed between neocortex
and allocortex and usually has six layers.
Allocortex typically has only one to four layers
of neurons and includes the hippocampal
complex (sometimes referred to as archicortex )
and primary olfactory cortex (sometimes
referred to as paleocortex ).
 Functional Divisions of the Cortex
• The lobes of the cerebral cortex have a variety of
functional roles in neural processing. Sometimes
we get lucky, and the gross anatomical
subdivisions of the cerebral cortex can be
related fairly to specific functions, such as in the
precentral gyrus where the primary motor
cortex resides.
• More typically, however, cognitive brain systems
are often composed of networks whose
component parts are located in different lobes
of the cortex.
 Motor Areas of the Frontal Lobe
• Among many other functions, the frontal lobe
plays a major role in the planning and
execution of movements. It has two main
subdivisions: the prefrontal cortex and the
motor cortex.
• The motor cortex sits in front of the central
sulcus, beginning in the depths of the sulcus
and extending anteriorly.
• These motor cortical areas contain motor
neurons whose axons extend to the spinal
cord and brainstem and synapse on motor
neurons in the spinal cord.
• The output layer of primary motor cortex
contains some of the most amazing neurons in
the nervous system: the large pyramidal
neurons known as Betz’s cells.
• Betz’s cells are the largest neurons in the
cerebral cortex.
Prefrontal Cortex
• The more anterior regions of the frontal lobe,
the prefrontal cortex , take part in the more
complex aspects of planning, organizing, and
executing behavior—tasks that require the
integration of information over time.
• The frontal lobe is often said to be the center of
executive function. People with frontal lobe
lesions often have difficulty reaching a goal.
• They may know the steps that are necessary to
attain it, but they just can’t figure out how to put
them together.
• Another problem associated with frontal lobe
lesions is a lack of motivation to initiate action,
to modulate it, or to stop it once it is happening.
• The main regions of the prefrontal cortex are
the dorsolateral prefrontal cortex , the
ventrolateral prefrontal cortex, the
orbitofrontal cortex and the medial prefrontal
regions, including the anterior cingulate
Cortex.
 Somatosensory Areas of the Parietal Lobe

• The parietal lobe receives sensory information from

the outside world, sensory information from within
the body, and information from memory, and
integrates it.
• Parietal lobe lesions result in all sorts of odd deficits
relating to sensation and spatial location: People
think that parts of their body are not their own or
parts of space don’t exist for them, or they may
recognize objects only from certain viewpoints, or
they can’t locate objects in space at all.
• Stimulating certain regions of the parietal lobe
causes people to have “out of body”
experiences (Blanke et al., 2002).
• Sensory information about touch, pain,
temperature sense, and limb proprioception
(limb position) is received via receptor cells on
the skin and converted to neuronal impulses
that are conducted to the spinal cord and then
to the somatosensory relays of the thalamus.
• From the thalamus, inputs travel to the
primary somatosensory cortex (or S1), a
portion of the parietal lobe immediately
caudal to the central sulcus.
• The next stop is the secondary somatosensory
cortex (S2), which is located ventrally to S1; S2
receives most of its input from S1. Together,
these cortical regions are known as the
somatosensory cortex.
 ****Visual Processing Areas in the
Occipital Lobe
• The business of the occipital lobes is vision. The
primary visual cortex is where the cerebral
cortex begins to process visual information.
• As mentioned striate cortex , V1 for visual area
1, or BA17. It receives visual information
relayed from the lateral geniculate nucleus of
the thalamus
• In humans, the primary visual cortex is on the medial
surface of the cerebral hemispheres, extending only
slightly onto the posterior hemispheric pole.
• Visual information from the outside world is
processed by multiple layers of cells in the retina and
transmitted via the optic nerve to the lateral
geniculate nucleus of the thalamus, and from there to
V1—a pathway often referred to as the
retinogeniculostriate , or primary visual pathway.
• The retina also sends projections to other subcortical
brain regions by way of secondary projection systems.
The superior colliculus of the midbrain is the main
target of the secondary pathway and participates in
visuomotor functions such as eye movements.
 Auditory Processing Areas in the Temporal
Lobe
• The auditory cortex lies in the superior part of the
temporal lobe in a region known as Heschl’s gyrus
within the Sylvian fissure) and roughly corresponds
with Brodmann areas 41 and 42.
• The auditory cortex has a tonotopic organization,
meaning that the physical layout of the neurons is
based on the frequency of sound.
• Neurons in the auditory cortex that respond best to
low frequency are at one end of the cortex, and
those that respond to high frequencies are at the
other.
• The projection from the cochlea (the auditory
sensory organ in the inner ear) proceeds
through the subcortical relays to the medial
geniculate of the thalamus and then to Heschl’s
gyri, the primary auditory cortex (A1) in the
supratemporal cortex.
• Surrounding and posterior to A1 is A2, the
auditory association area. BA22, which
surrounds the auditory cortex, aids in the
perception of auditory inputs; when this area is
stimulated, sensations of sound are produced in
humans.
 Association Cortex
• The portion of the neocortex that is neither
sensory nor motor cortex has traditionally been
termed the association cortex.
• These regions, which surround the identified
sensory or motor cortical process information
from the primary visual cortex about color,
simple boundaries, and contours to enable
people to recognize these features as a face
• Moreover, visual association cortex can be
activated during mental imagery when we call up
a visual memory even in the absence of visual
stimulation. Or, in the case of the auditory
system, the auditory association area is
necessary to recognize sounds.
• If that area is damaged, a person can still hear
sound but is unable to tell a dog’s bark from a
piano concerto.
 Blood Brain Barrier

• Approximately 20% of the blood flowing from the

heart is pumped to the brain. A constant flow of
blood is necessary, because the brain has no way of
storing glucose or extracting energy without oxygen.
• When the flow of oxygenated blood to the brain is
disrupted for only a few minutes, unconsciousness
and death can result.
• Two sets of arteries bring blood to the brain: the
vertebral arteries, which supply blood to the caudal
portion of the brain, and the internal carotid
arteries, which supply blood to wider brain regions
• Although the major arteries sometimes join
together and then separate again, little mixing
of blood occurs between the rostral and
caudal arterial supplies or between the right
and left sides of the rostral portion of the
brain.
• As a safety measure, in the event of a
blockage or ischemic attack, blood should be
rerouted to reduce the probability of loss of
blood supply; but in practice, this rerouting of
the blood supply is relatively poor.
• Blood flow in the brain is tightly coupled with
metabolic demand of the local neurons. Hence,
increases in neuronal activity lead to a coupled
increase in regional cerebral blood flow.
• Increased blood flow is not primarily for
increasing the delivery of oxygen and glucose
to the active tissue, but rather to hasten
removal of the resultant metabolic by-products
of the increased neuronal activity.
• local changes in blood flow permit regional
cerebral blood flow to be used as a measure
of local changes in neuronal activity, and serve
as the basis for some types of functional
neuroimaging.
• Particular examples are positron emission
tomography, using techniques such as the 15O-
water method, and functional magnetic
resonance imaging, which is sensitive to
changes in the concentration of oxygenated
versus deoxygenated blood in the region of
active tissue.