6.1 Definition and Localization of Integrative Functions



Integrative functions의 예: sleeping/waking cycle, consciousness, language, thinking
memory, learning, motivation, emotion
Brain area for integrative functions: neocortex and limbic system
Functional Topography of the Neocortex
Cerebral localization versus hollistic views
Gall, early 1800's: Prenology,
skull 모양을 보고 personality, mentality, moral characteristics 알수 있다고 주장
그러나 prenology는 no adequate scientific foundation
specific function(fx) of particular cortical areas:
1) Broca: motor speech center, 1865
2) primary motor cortex: Fritsch & Hitzig, 1870
3) sensory speech center: Wernicke, 1874

Fig. 6.1
Kleist: highly discrete localization of individual mental functions
Lashley: size of the lesion, rather than site: equipotentiality (hollistic)

Boundaries of the association cortex
Fig. 6.2
association cortex: the regions to which no predominant sensory or motor fx
can be assigned.
large part of the cerebral cortex
1) parietal-temporal-occipital association cortex
: higher sensory functions and language
2) prefrontal association cortex
: higher motor functions
3) limbic association cortex
: memory and emotional aspects of behavior
Limits of cerebral localization, definiton of centers

predominantly concerned with the specific function

Role of Encephalization in Higher Brain Functions
brain weight (E) = K X body weight (P)2/3; K: encephalization factor
K: mouse: 0.06
chimpanziees: 0.3
human: 1.00
evolutionaly development:
relative increase in the neocortex
--- reduction elsewhere in the brain
due to decreasing sensory specialization
& a need for fewer motor response patterns
hunter and prey: progressive encephalization in vertebrates, carnivores
present brain wt: 200,000 years ago, 1,400 g
language about 40,000 years ago
Superior thinking and learning abilities
<---- quantitative change, increase in the number of neuronal
aggregates available for information processing

6.2 General Physiology of the Cerebral Cortex



Functional Histology of the Cerebral Cortex
General arrangement of the cortex, cortical layers

multilayered, folded
total surface area: 2,200 cm2 (47 cm X 47 cm)
thickness: 1.3-4.5 mm
volume: 600 cm3
109 to 1011 neurons+ glial cells
striate appearance, 6 layers Fig. 6-3, 6-5
neocortex (isocortex)
allocortex: 3-layered (archipallium, paleopallium)

Fig. 6-3
I. Molecular layer (plexifrom layer)
numerous fibers (tangential), few cells
II. External granular layer
III. External pyramidal layer
IV: Internal granular layer
V. Interanl pyramidal layer
VI. Fusiform-cell layer

Cortical maps
structural pattern of the isocortex is uniform
variation: cortical cytoarchitectonics
Brodmann's 50 area Fig. 6-4










BRAIN FACTS

Homotypical and heterotypical isocortex
histological area = particular function
Von Economo: five basic types: 1,2,3,4,5, gradual transition
Fig. 6-5
homotypical cortex: 2,3,4; contain all 6 layers
heterotypical cortex: 1,5; fewer than 6 layers
1: agranular cortex; prototype of the motor cortex(ctx), efferent
5: granular cortex (koniocortex); prototype of the sensory ctx, affer
2: dysgranular cortex

Fiber connections in the neocortex

cortical efferents (corticofugal fibers)
1) projection fibers
2) association fibers
3) commissural fibers

cortical afferents (corticopetal fibers)
1) thalamocotical
2) association 3) commissural fibers

Cortical neurons and the circuits they form
2 main types: Fig. 6.6
pyramidal cells: pyramidal shape, axon leaves the ctx
stellate cells: stellate shape, cortical interneurons

Layer I:
apical dendrites of the pyramidal cells
axons of the stellate cells, tangential to the surface, local intracortical communication
afferent from nonspecific thalamus

Layers II & III:
small pyramidal cells, intercortical information transfer
afferents from nonspecific thalamus

Layer IV:
specific thalamic afferents (terminating on stellate, pyramidal cells
distribution to other layers

Layer V:
large pyramidal cell (giant cells of Betz in the motor ctx)
transfer of information to the subthalamic parts of the brain

Layer VI:
back to the thalamus, corticothalamic projection

perpendicular to the cortical surface:
processing particular kinds of information

concepts of histological and functional cortical columnar modules

Pyramidal cells:
apical dendrites: axodendritic synapses; excitatory
basal dendrites; inhibitory synapses

Stellate cells:
excitatory stellate cells: run perpendicular to the cortical surface
inhibitory stellate cells: parallel to the surface, basket-like
pericolumnar inhibition (basket cell)

various kinds of neurotransmitters

Electrophysiological Correlates of Cortical Activity

Biophysical properties of cortical neurons
Pyramidal cell:
resting membrane potential: -50 to -80 mV
action potentials: 60-100 mV in amplitude, 0.5-2 ms duration
originate at the axon hillock
axon을 따라, proximal dendrites, soma
up to 100 Hz
dendritic tree에서; dendritic generatting sites
fast prepotentials
(blocked by TTX, Na 채널)
slow dendritic action potentials
(blocked by Mg, Ca 채널)

Synaptic activity of cortical neurons

Excitatory postsynaptic potential (EPSP)
rise time: several ms
decay time: 10-30 ms
IPSP: 70-150 ms
less common than EPSP in the spontaneously active ctx
smaller amplitude
frequent long-lasting IPSP after activation of
the corticopetal sensory pathways.
frequency of cortical impulse activity elicited by PSP: low
usually below 10 Hz, not uncommonly below 1 Hz
resting potential: usually fluctuate in the range 3-10 mV
below threshold

Electrocorticograms (ECoG)
2 electrodes laid on the surface of the cerebral ctx
Fig. 6-7
continuous potential fluctuations, 1 - 50 Hz, 100 μV or more
normal conditions: frequency & amplitude
: species of animal, recording site, degree of wakefulness
in humans: awake but relaxed state, 8-13 Hz, occipital ctx, alpha waves
eyes open: alpha blockade, replaced by beta waves; 14-30 Hz
lower amplitudeOrigin of the ECoG
reflects the postsynaptic activity of the cortical neurons
positive potential fluctuation: EPSPs in the deeper layers of the ctx
IPSPs in the superficial layers
negative potential fluctuation: 반대로

rhythmic activity of the ctx (alpha rhythm)
: induced largely by the activity of the deeper structures (thalamus)
Fig. 6-8
ablation of thalmus, deafferentation---> alpha 리듬 사라짐
decortication: no change in alpha rhythm
multiple thalamic pacemakers
reticular structures: synchronizing & desynchronizing action

Event-related potentials, ERPs
characteristic potential fluctuations that tend to appear after
psychological, motor and sensory events.
e.g.: rediness potential, expectancy potential, premotor positivity
Evoked potentials (EPs):
receptors (sensors), peripheral nerves,
sensory tracts, nuclei, other sensory structures를 자극시 출Fig. 6-9:
somatic evoked potentials (SEPs)
: peripheral somatic nerve를 자극, recording from SI, SII
Primary evoked potential: from postcentral gyrus의 작은 지역
Secondary evoked potential: from extensive cortical region

origin of EP: reflection of the synaptic activity


The main value of EP measurement for clinical diagnosis
to test the intactness of peripheral sensory and subcortical pathways

Fig. 6.10: Auditory evoked potential (AEP)
6 distinct positive peaksI: auditory nerve
II: cochlear nucleus
III: superior olive
IV & V: lateral lentiform nuclei, & inferior colliculi
VI: thalamic level
Visual EP (VEP)

Electroencephalogram (EEG)

Definition, mechanism of origin
1929-1938: Hans Berger
scalp에서, smaller amplitude & lower frequency
mechanism: same as ECoG

Recording and interpreting the EEG
standardized, recording site, recording conditions: Fig. 6.11
interpretation based on: Fig. 6.12
frequency, amplitude, shape and distribution of the waves in the EEG
proportions of the different kinds of waves

Forms of the EEG; diagnostic significance
Fig. 6.11
alpha waves: alpha rhythm: 8-13 Hz (10 Hz), eyes closed, occipital area
synchonized EEG
alpha blockade, eyes open
beta waves: 14-30 Hz (20 Hz), smaller amplitude, desynchronized EEG
theta waves: 4-7 Hz (6 Hz)
delta waves: 0.3-3.5 Hz (3 Hz)
slow waves during sleeping
EEG of children and adolescent: slower, more irregular,
exhibiting delta waves even in waking state

EEG: the only available method for the continuous quantification of
neuronal processes in the intact human brain
: the most important means of access to human information processing
and behavior-controlling mechanisms for both psychological and
clinical practice

Fig. 6.12seizure potentials, cerebral trauma, metabolic intoxication
tumors, diffuse organic brain disease, psychoactive drug

isoelectric or flat EEG: a criterion for death
cortex (3-8 min) and brainstem (7-10 min): low ischimia tolerance
resuscitation limit
myocardium: 20 min, kidney: 150 min
organ transplants

Magnetencephalography, MEG

brain generates weak magnetic field
better spatial resolution of the site of origin of cortical activity
at present for research use

Cerebral Activity, Metaboilism and Blood Flow
brain consumes about 50 ml oxygen/min:
resting person에서, 대개 20% of the total oxygen requirement
15% of the cardiac output at rest
rate of perfusion is not uniform in all parts of the brain
cerebral cortex >>> white matter
Fig. 6.14
alpha wave EEG시: blood flows: frontal regions >> other areas
slight pain ---> primary sensory area
hand movment---> "
metabolic maps: monitoring the uptake of radioactive glucose
parallel with the changes of the regional blood-flow maps
regionally elevated neuronal activity---> local vasodilation

Imaging Procedures for the Representation of Brain Structures and Activities

X-ray computed tomography (CT)
0.5-1 mm resolution for a layer 2-13 mm thick
positron-emission tomography (PET)
4-8 mm spacial resolution, temporal resolution of 1 s

tomography by nuclear magnetic resonance (NMR)1 mm resolution, thickness: 5-10 mm, temporal resolution: 10-20s










BRAIN FACTS