Brain Functional Organization

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Brain Functional Brain Functional OrganizationOrganization

Janusz A. Starzyk

http://grey.colorado.edu/CompCogNeuro/index.php/CECN_CU_Boulder_OReillyhttp://grey.colorado.edu/CompCogNeuro/index.php/Main_Page

Based on book Cognition, Brain and Consciousness ed. Bernard J. Baars

courses taught by Prof. Randall O'Reilly, University of Colorado, andProf. Włodzisław Duch, Uniwersytet Mikołaja Kopernikaand http://wikipedia.org/

Cognitive ArchitecturesCognitive Architectures

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IntroductionIntroduction 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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RulesRules 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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MacrolevelMacrolevel

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 approximatedifferentiation, yielding representation invariance, specialization and

hierarchy.

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Hierarchy and specializationHierarchy and specializationMental 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 interactionDistribution and interactionSpecialization 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 principlesDynamic principlesWell-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 arrowFruit 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 SystemThe Nervous System

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 brainGeography of the brain 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 brainGeography of the brain 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 cortexGeneral 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 classificationsBrodmann 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.

Lateral left panel and right Mid-sagittal view

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The layers of the cortexThe 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 cortexThe layers of the cortex (cont.)(cont.)

Different types of neurons in the visual cortex and which regions of the brain they connect.

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Growth of the brainGrowth 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 brainEvolutionary diagram of the brain

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 removed.

MRI of 7-year old girl with her left hemisphere removed at age of 3.

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Anatomy of the brainstem and ponsAnatomy 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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ThalamusThalamus

Two egg-shaped thalami form the upper part of the brain stem

Middle view of the hypothalamus and surrounding regions

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HippocampusHippocampus

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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AmygdalaAmygdala

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 GangliaBasal Ganglia

Basal ganglia plays a crucial role in controlling movement and cognition.

Basal ganglia are shield-like structures outside of each thalamus and have outside radiating tubes called putamen.

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Cerebral hemispheresCerebral hemispheres

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 areasSubcortical 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 areasSubcortical areas

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.

Basal ganglia (striatum, globus pallidus, substantia nigra)Basal ganglia initiate motor activities and the substantia nigra is responsible for controlling learning

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Bottom view of the brainBottom view of the brain

Notice the optic nerve linking eyes to the cortex

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The cerebral hemispheresThe 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 callosumThe 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 controlCortical 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 the world or self in humans

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Development Development of the brainof the brain

Development stages of the human brain from conception of life to birth

real size

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Input and output in the cortexInput and output in the cortex

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 cortexRepresentation of the body areas in the cortex

Sematosensory and motor cortex are next to each other on both sides of the central sulcus

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Representation of the body areas in the cortexRepresentation of the body areas in the cortex

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 visibleMajor lobes – hidden and visible

Four visible lobes: frontal, parietal, temporal and occipital plus two hidden lobes: insula and median temporal lobe.

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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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, shape, depth, visual associations

Major lobes – hidden and visibleMajor lobes – hidden and visible

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     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.

Major lobes – hidden and visibleMajor lobes – hidden and visible

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Functioning of parietal lobe.Functioning of parietal lobe.

Schematic association of multisensory function of the parietal lobe.Schematic association of multisensory function of the parietal lobe.

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 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.

Major lobes – hidden and visibleMajor lobes – hidden and visible

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     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.

Major lobes – hidden and visibleMajor lobes – hidden and visible

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Connections between the cortex and thalamusConnections between the cortex and thalamus

All inputs and outputs to the brain go through thalamus

A color-coded schematic showing the mapping of the thalamus to cortical regions

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Major fiber patterns in the brainMajor 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 Projections of the Ascending Reticular Activating System (ARAS)Activating System (ARAS)

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 architectureCognitive architecture

Hierarchical structure for sensory data, recurrence in FC, recording

the context.

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Activity 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

effects of the interaction of different areas.

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Controlled/automatic actionControlled/automatic actionAutomatic: 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 - consciousnessOther 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 problemsVarious potential problemsThere 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 integrationProblem 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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ChallengesChallenges 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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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.

SummarySummary