Transcript Brain Functional Organization

Cognitive Architectures
Brain Functional
Organization
Based on book Cognition, Brain and Consciousness ed. Bernard J. Baars
courses taught by Prof. Randall O'Reilly, University of Colorado, and
Prof. Włodzisław Duch, Uniwersytet Mikołaja Kopernika
and http://wikipedia.org/
http://grey.colorado.edu/CompCogNeuro/index.php/CECN_CU_Boulder_OReilly
http://grey.colorado.edu/CompCogNeuro/index.php/Main_Page
Janusz A. Starzyk
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Introduction
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The brain gave humans the biggest evolutionary
advantage over other animals
The brain has several interacting major organs:
cortex, thalamus, basal ganglia, cerebellum ,
hippocampus, limbic regions, etc.
The closest connections are between cortex and
thalamus.
Cortex contains many billions of neuron cells
known as gray matter connected through billions
of connections known as white matter.
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Rules
 The brain is not a universal computer.
 Neurons adjusted evolutionally to detect specific properties of
analyzed signals.
 Compromise between specificity and built-in expectations, and
generality and universality.
 Compromise between speed of the hippocampus representing
temporal sequences, and slowness of the cortex integrating many
events.
 Compromise between active memory and control of understanding.
How to build, using neurons, all necessary elements - specific and
universal?
Dynamic rules on the macro level:
 Constraint satisfaction (including internal), knowledge a priori.
 Contrast reinforcement, attractors, active memory.
 Attention mechanisms, inhibitory competition.
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Macrolevel
Neuron-detector layers strengthening/weakening differences.
 Hierarchical transformation sequences.
 Special transformations for different signals.
 Specialized information transfer pathways.
 Interactions within pathways.
 Processing and memory built into the same hardware
 Higher-level association areas.
 Distributed representations across large areas.
Strong feedback between areas causes this to be only approximate
differentiation, yielding representation invariance, specialization and
hierarchy.
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Hierarchy and specialization
Mental processes: the result of hierarchical and specialized
transformation of sensory signals, internal states (categories)
and undertaken actions.
Neuron-detector layers process signals coming to them from receptors,
strengthening/weakening differences.
Emerging internal states provide interpretations of environmental states
- hierarchical processing is necessary to attain invariant
representations, despite variable signals, eg. aural (phonemes), or
visual (colors, objects).
Transformations and specialized information processing streams
stimulate internal representations of categories and provide data for
taking action, e.g. motor reactions. Simultaneously, processed
information modifies the means of information processing.
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Distribution and interaction
Specialization increases efficiency of activity, but interactions between
streams are essential for coordination, acquiring additional stable
information on different levels, e.g.. spatial orientation and object
recognition.
On a higher level we have heterogenic association areas.
Knowledge linked to recognition
(e.g. reading words) is distributed
across the whole brain, creating a
semantic memory system.
It's similar on a micro and macro
level: interpretation of the whole is
the result of distributed activity of
many elements.
Knowledge = processing,
Program ~ data.
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Dynamic principles
Well-known inputs trigger an immediate reaction.
New ones may require iterative searches for the best compromise
satisfying constraints resulting from possessed knowledge = possible to
attain dynamic states of the brain.
There exist many local, alternative or sub-optimal, solutions
=> local context (internal) changes the interpretation.
Time flies like an arrow
Fruit flies like a banana
Long-term memory is the result of learning, this is synaptic memory.
Active memory (dynamic) is the result of momentary mutual activations
of active areas; it's short-term because the neurons get tired and are
involved in many processes; this directly influences processes in other
areas of the brain.
This mechanism causes the non-repeatability of experiences = internal
interpretations, contextual states are always somewhat diverse.
Concentration is the result of inhibitory interactions.
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The Nervous System
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The brain is a part of the
nervous systems which
controls nearly everything
in our bodies.
The main two parts are
central nervous system
(CNS) and peripheral
nervous system (PNS)
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Geography of the brain
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The outer layer, or cortex, of the brain is made up of
four major lobes – frontal parietal, temporal and
occipital.
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Geography of the brain
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There are many other important “landmarks” used to
identify the brain regions.
Lateral left panel and
right Mid-sagittal view
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General functions of the cortex
Brodmann's areas
of the cortex
Four cortical lobes
and their functions
Various terms used to refer to locations in the brain
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Brodmann region classifications
Broadman areas - left and right hemispheres.
 Over 100 specialized regions were recognized.
 They are responsible for audio, vision, motor,
olfaction, language, cognition, etc.
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Lateral left panel and
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right Mid-sagittal view12
The layers of the cortex
The neocortex has the six major layers
organized in cortical columns.
 Layer I consists mostly dendrites (input
fibers).
 Columns may be clustered into
hypercolumns.
 The image is based on Area 17 of the
V1 visual cortex.
 The paleocortex (older region of cortex)
has five layers.
 Neurons in cortex grow, migrate,
connect, disconnect, and die changing
its topology and function.
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The layers of the cortex (cont.)
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Different types
of neurons in
the visual
cortex and
which regions
of the brain
they connect.
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Growth of the brain
Starts with the brainstem
with the thalami as the
major input hub
 Next is the hippocampus
 Followed by fluid ventricles
(central to the brain’s
circulatory system).
 Basal ganglia are next (can
be thought of as the output).
 White matter (the
interconnective material –
myelin sheathed axons)
 Last is the gray matter (outer
body of the cortex).
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Evolutionary diagram of the brain
MRI of 7-year
old girl with
her left
hemisphere
removed at
age of 3.
Evolution of the mammalian brain.
 Cortex is flexible and can resume various functions
particularly at early stage in life
 Brainstem is crucial to life functions and cannot be
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removed.
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Anatomy of the brainstem and pons
The brain stem
is continuous
with the spinal
cord.
 Some basic
functions like
breathing and
heart rate are
controlled here.
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Thalamus
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Two egg-shaped
thalami form the upper
part of the brain stem
Middle view of the hypothalamus
and surrounding regions
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Hippocampus
On a top of thalami are two
hippocampi – one on each
side.
 Hippocampus plays
important role in transferring
experienced information to
long term memory and
retrieving episodic memory.
 It is also involved in spatial
navigation.
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Amygdala
At the end of each
hippocampus are amygdalas.
 Amygdala plays a crucial role
in emotions and emotional
associations.
 Four ventricles above contain
cerebrospinal fluid that
descends to the spinal cord
though tiny aqueduct .
 In the ventricular walls neural
stem cells are developed to
produce new neurons.
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Basal Ganglia
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Basal ganglia are
shield-like structures
outside of each
thalamus and have
outside radiating tubes
called putamen.
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Basal ganglia plays a crucial role in controlling movement
and cognition.
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Cerebral hemispheres
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On top of the lower
levels of the
brainstem, thalami,
hippocampi, and
amygdala, ventricles
and basal ganglia are
two hemispheres.
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Subcortical areas
Brain stem:
raphe nuclei: serotonin,
reticular formation: general
consciousness.
Midbrain: (mesencephalon):
part of the ventral tegmental
area (VTA): dopamine,
value of observation/action.
Thalamus: input of sensory signals, attention
Cerebellum: learning motion, temporal sequences of motion.
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Subcortical areas
Basal ganglia (striatum, globus
pallidus, substantia nigra)
Basal ganglia initiate motor
activities and the
substantia nigra is responsible for
controlling learning
 Amygdala: emotions, affective associations.
 Basal ganglia: sequences, anticipation, motor
control, modulation of prefrontal cortex activity,
selection and initiation of new activity.
 Hippocampus: fast learning, episodic and spatial
memory.
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Bottom view of the brain
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Notice the optic nerve linking eyes to the cortex
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The cerebral hemispheres
Two mirror-image halves of
the brain cortex puzzled
philosophers since they
expected that a brain will
have some central feature
responsible for the soul.
 The cerebral hemispheres
are linked by the fiber tract
called corpus callosum.
 100 mln axons run between
two hemispheres
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The corpus callosum
Many aspects of
sensory and motor
processing cross
over information
from left to right
hemisphere.
 Only the (very old)
olfactory nerve
stays on the same
side of the cortex.
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Cortical control
The cortical output control also crosses over to the
opposite regions of the body.
 However, separation of the two hemispheres by cutting
the corpus callosum does not change perception of the28
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world or self in humans
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Development
of the brain
real size
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Development
stages of the
human brain
from
conception of
life to birth
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Input and output in the cortex
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Cortex is a folded sheet
of gray matter 60x60 cm.
It is folded into hills (gyri)
and valleys (sulci).
Sensory parts are placed
in 3 lobes posterior to
central sulcus and
Sylvian fissure.
Parietal lobe contains
sematosensory and
associative areas
Temporal lobe contains
auditory cortex
Occipital lobe contains
visual cortex.
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Representation of the body areas in the cortex
Sematosensory and motor cortex are next to each other on
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both sides of the central sulcus
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Representation of the body areas in the cortex
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Wilder Penfield at University of Montréal established
sematosensory and motor maps by electrically stimulating
patients.
For sematosensory stimulation patients would feel a touch
in the corresponding part of the body.
Stimulation of the motor area would evoke specific body
movement, but patients would deny control of these
movements.
When the doctor asked – are you moving your hand? – the
patient answered – no you are moving my hand.
However stimulation of the premotor area (1 cm anterior)
would evoke a reported intention to move a corresponding
part of the body without a sense of being externally
controlled.
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Major lobes – hidden and visible
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Four visible lobes:
frontal, parietal,
temporal and occipital
plus two hidden lobes:
insula and median
temporal lobe.
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Brain directions: front, back, upper, and lower are also named
as: rostral (or frontal), caudal (or posterior), dorsal (or
superior), and ventral (or inferior).
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Major lobes – hidden and visible
Four visible lobes of the
cortex:
frontal lobe
occipital lobe
parietal lobe
temporal lobe
The frontal lobe is responsible for: planning, thinking, memory,
willingness to act and make decisions, evaluation of emotions and
situations, memory of learned motor actions, e.g. dance, mannerisms,
specific patterns of behavior, words, faces, predicting consequences,
social conformity, tact, feelings of serenity (reward system),
frustration, anxiety and stress.
The occipital lobe is responsible for: sight, analyzing colors, motion,
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shape, depth, visual associations
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Major lobes – hidden and visible
parietal lobe
temporal lobe
The parietal lobe is responsible for: spatial orientation, motion
recognition, feeling temperature, touch, pain, locating sensory
impressions, integration of motion, sensation and sight, understanding
abstract concepts.
The temporal lobe is responsible for: speech, verbal memory, object
recognition, hearing and aural impressions, scent analysis.
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Functioning of parietal lobe.
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Schematic association of multisensory function of the parietal lobe.
Major lobes – hidden and visible
insula and Sylvian fissure
Insula is responsible for: ‘gut feelings’ like sense of nausea and disgust,
interoception (feeling internal organs), emotional awarness.
Sylvian fissure runs between parietal and temporal lobes horizontaly
towards junction with occipital lobe. It contains supratemporal plane that
hosts primary and secondary auditory cortex and part of Wernicke’s area
for speech comprehension.
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Major lobes – hidden and visible
medial temporal lobe
The medial temporal lobe is a part of temporal lobe but has different
anatomy. It contains hippocampi and related regions that are associated
with episodic memory. It contains limbic system with cingulate sulcus
involved in resolving conflicting situations and rhinal sulcus responsible
for smell. It is an older part of cortex with only 5 layers and is sometimes
referred to as paleocortex.
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Connections between the cortex and thalamus
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All inputs and outputs
to the brain go through
thalamus
A color-coded schematic showing the mapping of the thalamus to
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cortical
regions
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Major fiber patterns in the brain
Fibers from cortical cells spread in every direction
between hemispheres, thalamus, and other brain
organs
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Projections of the Ascending Reticular
Activating System (ARAS)
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The ARAS and extended
reticular-thalamic system
(ERTAS) are thought to be
required for the normal
conscious waking state.
Various sensory inputs
converge in this region and
compete.
If an input prevails it becomes a
global message distributed to
other brain areas.
Thus ERTAS underlies ‘global
broadcasting’ function of
consciousness of a selected
sensory input.
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Cognitive architecture
Hierarchical structure for sensory data, recurrence in FC, recording the
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context.
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Activity
Parietal cortex: learns slowly, creates extensive, overlapping
representations in a densely connected network.
Dynamic PC states are short-term memory, mainly of spatial relations,
quickly yielding to disorder and disintegration.
Frontal cortex: learns slowly, stores isolated representations, activation of
memory is more stable, the reward mechanism dynamically switches its
activity, allowing a longer active memory.
The hippocampus learns quickly, creating sparse representations,
differentiating even similar events.
This simplified architecture will allow the modeling of many
phenomena relevant to perception, memory, using language, and the
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effects of the interaction of different areas.
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Controlled/automatic action
Automatic: routine, simple, low level, sensory-motor, conditional reflexes,
associations – easy to model with a network.
Controlled: conscious, elastic, requiring sequences of actions, selection
of elements from a large set of possibilities – usually realized in a
descriptive way with the help of systems of rules and symbols.
Models postulating central processes: like in a computer, working
memory with a central monitor, having influence over many areas.
Here: emergent processes, the result of global constraint fulfillment, lack
of a central mechanism.
The prefrontal cortex can exert control over the activity of other areas, so
it's involved in controlled actions, including the representation of "me" vs.
"others", social relationships etc.
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Other distinctions - consciousness
 Declarative vs. procedural knowledge
Declarative: often expressed symbolically (words, gestures).
Procedural: more oriented towards sequences of actions.
 Explicit vs. implicit knowledge
Controlled action relies on explicit and declarative knowledge.
Automatic actions rely on implicit and procedural knowledge.
Consciousness => states existing for a noticeable period of time,
integrating reportable sensory information about different modalities,
with an influence on other processes in the brain.
 Each system, which has internal states and is complex enough to
comment on them, will claim that it's conscious.
 Processes in the prefrontal cortex and the hippocampus can be
recalled as a brain state or an episode, can be interpreted
(associated with concept representation).
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Various potential problems
There are easy things, for which simple models will suffice, and difficult
things requiring detailed models.
Many misunderstandings: MLP neural networks are not brain models,
they are only loosely inspired by a simplified look at the activity of neural
networks; an adequate neural model must have appropriate architecture
and rules of learning.
Example: catastrophic forgetting of associations from lists, much
stronger in MLP networks than in people => appropriate architecture,
allowing for two types of memory (hippocampus + cortex) doesn't have a
problem with this.
Human cognition is not perfect and good models allow us to analyze the
numerous compromises handled by the brain.
Brains are fairly elastic, although they mostly base their actions on the
representation of specific knowledge about the world.
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Problem of integration
 Binding problem: we perceive the
world as a whole, but information in
the brain, after initial processing,
doesn't descend anywhere.
 Likely synchronization of distributed
processes.
 Attention is a control mechanism
selecting areas which should be
active in a given moment.
 Encoding relevant combinations of
active areas.
Simultaneous activity = dynamic synchronization, partial reconstruction
of the brain state during an episode.
Integration errors happen often.
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Challenges
 Disruptions: Multi-level transition from one activity to another and
back to the first, or recurrent multiple repetition of the same activity.
 This is easy for a computer program (loops, subroutines), where
data and programs are separated, but it's harder for a network,
where there is no such separation.
 PFC and HCMP remember the previous state and return to it.
 Difficult task, we often forget what we wanted to say when we listen
to someone, sentences are not nested too deeply.
The rat the cat the dog bit chased squeaked.
How and what should be generalized? Distributed representations
connect different features.
Dogs bite, and not only Spot, not only mongrels, not only black dogs...
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Summary
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We discussed basic structures and regions of the brain and
their role in human cognition.
Remember that brain developed over millions of years and
changed through time.
Newer, more advanced parts of the brain are built around
and on the top of the older brain.
Cortex or neocortex represents recent development in the
human brain and the frontal and parietal lobes are
expanded comparing to other primates.
Brain is highly interconnected with millions of fibers linking
two hemispheres.
There is no clear explanation why brain has dual structure.
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