IV.Brain Function II: Evidence from Neuroanatomy and Perception Brain, Mind, and Belief: The Quest...

IV. Brain Function II: Evidence from Neuroanatomy and Perception

Brain, Mind, and Belief: The Quest for Truth

“Our neural pathways establish reruns of what has gone on before. Like the three-year-old who insists on watching The Little Mermaid over and over again, we cling to our warped illusions with a tenacious grip. Get your bloody hands off my illusion! Even though it makes us miserable, we prefer to place our faith in the disaster we have made.”                                                                  Pam Grout

Where we have been

Figuring out how the brain works Methods in general use

• Lesion studies• Functional brain imaging

Guiding principles in current use• Tool-driven inquiry

Functional brain imaging• Misapplied metaphor

The brain is a computer A better way

• Think harder• Use evidence from linguistics

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Thinking harder

Avoid metaphorical thinking• The brain is not a computer• Not like a human being with paper & pencil & books• In fact it is not like anything else

It is itself: the brain

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REVIEW

Where we are

The mind is a relational network system• As revealed by evidence from linguistics

We can study relational networks at different levels of precision• Abstract network notation• Narrow network notation

Hypothesis:• Relational networks are implemented in

neural structures

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Levels of precision

Abstract relational network notation Narrow relational network notation Neural structures

• A node of narrow RN notation is implemented physically as a bundle of neurons

Where we are headed

Consider further evidence• Neuroanatomy • Perceptual neuroscience

Examine further findings on perception

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Functional bundles of neurons:Cortical columns

Vernon Mountcastle, Perceptual Neuroscience (1998), p. 192

“[T]he effective unit of operation…is not the single neuron and its axon, but bundles or groups of cells and their axons with similar functional properties and anatomical connections.”

The cortical (mini)column

Compare: atom and molecule :: neuron and column of neurons

Molecule: a bundle of atoms that function together as a unit

Cortical Column: a bundle of neurons that function together as a unit

Gray matter and white matter

Gray matter

White matter

Coronal section magnified

From top to bottom, About 3 mm Has 6 layers

Microscopic views

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Different stains show different features

The node of narrow RN notationvis-à-vis neural structures

The node corresponds not to a single neuron but to a bundle of neurons

The cortical column A column consists of 70-100 neurons

stacked on top of one another All neurons within a column act together

• When a column is activated, all of its neurons are activated

Large-scale cortical anatomy

The cortex in each hemisphere • Appears to be a three-dimensional structure• But it is actually very thin and very broad

The grooves – sulci – are there because the cortex is “crumpled” in order to fit inside the skull

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Topologically, the cortex of each hemisphere (not including white matter) is..

Like a thick napkin, with• Area of about 1300 square centimeters

200 sq. in. 2600 sq cm for whole cortex

• Thickness varying from 3 to 5 mm• Subdivided into six layers

Just looks 3-dimensional because it is “crumpled” in order to fit inside the skull

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Topological essence of cortical structure

Each column represents a node The network is thus a large two-dimensional array of nodes Third dimension for

• Internal structure of the nodes (columns)• Cortico-cortical connections (white matter)

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Neurons, Columns, Cortex

At the small scale..• Each column contains around 80 neurons

At a larger scale..• Each column acts as a node of the cortical network

The cerebral cortex as an array* of columns:• Grey matter — columns of neurons• White matter — inter-column connections

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*Array: two dimensional (a lot simpler than 3-dimensional)

Composition of a typical minicolumn

Contains about 80 neurons• Range: 70 to 110• Mostly pyramidal neurons

Cell bodies of these neurons are “stacked” vertically• (i.e., in a column – hence the name)

Fibers extending from the cell bodies• Many are vertical (especially those of pyramidal cells)• Some are horizontal

They connect to neighboring columns

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Evidence for columns

Microelectrode penetrations of cortex• Electrode is small enough to detect activation

in a single neuron If perpendicular to cortical surface

• Neurons all of same response properties If not perpendicular

• Neurons of different response properties

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Column in a cat’s cortex fora point on the cat’s paw

Columns as functional units:Orientation of lines (visual cortex)

Microelectrode penetrations

K. Obermayer & G.G. Blasdell, 199320

Bundles of columns

Minicolumn – 30-50 microns diameter Maxicolumn – a contiguous bundle of minicolumns

(typically around 100)• 300-500 microns diameter• Dimensions vary from one part of cortex to another• In some areas at least, they are roughly hexagonal

(There are also larger bundles)

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Columns of different sizes

View: looking downward from top of column. So each circle represents a column

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Minicolumn Largercolumn

Cortical minicolumns: Quantities

Diameter of minicolumn: 30 microns Neurons per minicolumn: 70-110 (avg. 75-80) Minicolumns/mm2 of cortical surface: 1460 Minicolumns/cm2 of cortical surface: 146,000 Neurons under 1 sq mm of cortical surface: 110,000 Approximate number of minicolumns in Wernicke’s

area: 2,920,000 (at 20 sq cm for Wernicke’s area) • (Wernicke’s area is devoted to speech recognition)

Cf. Mountcastle 1998: 96

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Cortical column operation

The linguistic system operates as a network whose nodes are cortical columns

Columns do not store symbols Their basic function: receive and send activation

• Integration: A column is activated if it receives enough activation from other columns

Can be activated to varying degrees Can keep activation alive for a period of time

• Broadcasting: An activated column transmits activation to other columns

Excitatory – contribution to higher level Inhibitory – dampens competition at same level

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Integration and Broadcasting

Integration

Broadcasting

Wow, I got activated!

Now I’ll tell my friends!

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Operations in neurocognitive networks

Activation moves along lines and through nodes (along the pathways of the brain)

• Integration • Broadcasting

Connection strengths are variable• A connection becomes stronger with repeated

successful use• A stronger connection can carry greater activation

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Basic answer to the what/how question:What goes on in those nodes of the network?

Broadcasting• To multiple locations• In parallel

Integration

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Integration and Broadcasting

Part of the network for FORK

V

C

Each node in this diagramrepresents a cortical column

M

T

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C — conceptualM — motorT — tactileV — visual

Part of the network for FORK

V

C

Each node in this diagramconnects to a supporting subnet. For example,

Let’s zoom in on this one

M

T

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Zooming in on the “V” Node..

FORK

Etc. etc.(many layers)

A network of visual features

V

The cardinal node of this subnet

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Some nodes of the cortical net for fork

V

M CT

P

Au

Ar

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Ar – ArticulationAu – AuditoryC – ConceptualM – MotorP – PhonologicalT – TactileV – Visual

Some nodes of the cortical net for fork

V

M CT

P

PA

PP

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Perception: the basic process

A bottom-up process• From primary perceptual area upwards

E.g. primary auditory, for auditory perception Multiple steps of integration and broadcasting

Takes place in a perceptual area of cortex• E.g. auditory cortex for auditory perception

Works by integrating inputs to the associated sense organ• E.g. auditory input for auditory perception• Multiple steps of integration

From very simple To more complex

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Perception: Multiple steps of integration and broadcasting

DOG

From lowerlevels up to higher levels

V

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These are cortical (network) structures that have to be learned

Experiment by David Hubel and Torsten Wiesel

Kittens kept in dark room during critical period for developing vision

Exposed to vertical lines but not horizontal lines

Later, bumped into strings stretched horizontally in their path• Couldn’t see them

Their eyes received the information

But their brains couldn’t integrate it 35

Hints of what goes on in visual perception(multiple steps of integration and broadcasting)I: Shapes recognized by different low level columns

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Hints of what goes on in visual perception(multiple steps of integration and broadcasting)II. Relatively higher level (but still quite low)

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Hints of what goes on in visual perception(multiple steps of integration and broadcasting)III. At a somewhat higher level

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Hints of what goes on in visual perception(multiple steps of integration and broadcasting)IV. Somewhat higher level

Elementary shapes like these..

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Hints of what goes on in visual perception(multiple steps of integration and broadcasting)IV. Somewhat higher level

..can be integrated into more complex formations

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We see only the past

Perception is a bottom-up process• From primary perceptual area upwards

Step by step through multiple levels• Using network connections that have been established• These connections have been built step by step

From lower levels to higher levels As a result of previous experience

The whole perceptual structure is built through experience• Therefore, it is based upon the past

Hence, we see nothing as it is now

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Returning to work after 30 years

Playvideo

http://www.youtube.com/watch?v=mFCCFS_lhA8

Perception: Refining the starting (simple) view

The simple (starting) view:• A single perceptual modality

Auditory perception in auditory cortex using auditory information

Step by step from bottom up Complications/Refinements

1 It is not confined to a single perceptual modality2 Not just bottom-up3 Not even confined to posterior cortex

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The McGurk Effect

Acoustic syllable [ba] presented to subjects with visual presentation of articulatory gestures for [ga] Subjects typically heard [da] or [ga] “Evidence has accumulated that visual speech modifies

activity in the auditory cortex, even in the primary auditory cortex.”

Mikko Sams (2006)

http://www.youtube.com/watch?v=aFPtc8BVdJk

How does it work? (1) Visual input(2) Top-down processing

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Refining the starting (simple-minded) view: I

1. It is not confined to a single perceptual modality• Example: The McGurk effect

Auditory perception affected by visual input i.e., top-down processing from visual to auditory

• Conceptual structure affects auditory perception The influence of context on speech perception

She cooked it in the frying an I’ll help you if I an

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An important finding from neuroanatomy: Reciprocal connections

An established fact of neuroanatomy:• A connection from point A to point B in

the cortex is generally accompanied by a connection from point B to point A

Separate fibers (axons): (1) A to B, (2) B to A In short, cortico-cortical connections are

generally bidirectional Hence, Bidirectional Processing

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AB

Bidirectional processing: reciprocal links

excitatory

inhibitory

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Perception – Refining a simple-minded view: II

1. Not confined to a single perceptual modality• Example: The McGurk effect

Visual input affects auditory perception• Conceptual structure affects auditory perception

2. Not just bottom-up• Top-down processing fills in unsensed details

3. Not even confined to posterior cortex

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Perception: All these lines represent bi-directional connections

DOG

Etc. etc.(many layers)

V

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A terminological problem

We need to distinguish• Perception narrowly conceived

The basic process of recognition Single perceptual modality Bottom-up processing No motor involvement

• Perception broadly conceived Two different terms needed

• Recognition (a.k.a. ‘microperception’) Bottom-up process in a single perceptual modality

• Perception (the broad conception) (a.k.a. ‘macroperception’)

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“Micro-perception” and “macro-perception”

Microperception and macroperception Microperception

• A.k.a. recognition• The local process of integrating features• Performed in one perceptual modality• Bottom-up

Macroperception• The overall process of perception• Uses multiple modalities• Uses top-down processing

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Perception – Refining a simple-minded view

1. Not just bottom-up• Top-down processing fills in unsensed details

2. Not confined to a single perceptual modality• The McGurk effect

Visual input affects auditory perception• Conceptual structure affects auditory perception

3. Not even confined to posterior cortex• Can also use motor neurons (frontal cortex)

Experiment: left hand or right hand? Mirror neurons

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Left hand or right hand?

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Left hand or right hand?

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Left hand or right hand?

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Left hand or right hand?

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Left or right hand?

How do you do it? Imaging experiment Subjects were shown pictures of one hand Asked to identify: left or right Functional imaging showed increased CBF in

hand area of motor cortex

Peter Fox, ca. 2000

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Motor structures in perception

The left-hand vs. right-hand experiment ‘Mirror neurons’ in motor cortex Articulation as aid to phonological perception Articulation in reading Motor activity in listening to music Watching an athletic event

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Mirror Neurons

NY Times: “One mystery remains: What makes them so smart?” (Jan. 10, 2006)

Answer: They are not smart in themselves• Their apparent smartness is a result of

their position: at top of a hierarchy• Compare:

The general of an army The head of a business

Similarly, high-level conceptual nodes• The “cardinal node”

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Mirror Neurons

What makes mirror neurons appear to be special?• Ans.: They receive input from visual perception• The superior longitudinal fasciculus

Connects visual perception to motor areas How can a motor neuron receive perceptual input?

• Motor neurons are supposed to operate top-down• Answer: bidirectional processing

They also receive perceptual information• Bottom-up processing

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Superior Longitudinal Fasciculus

From O. D. Creutzfeldt, Cortex Cerebri (1995) 61

Are some neurons “smarter” than others?

Alternative: the head of a dedicated net• Dedicated nets have hierarchical structure• It is the hierarchy as a whole that has those ‘smarts’• Similarly, mirror neurons

They get visual input since they are connected to visual areas• Superior longitudinal fasciculus

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Implications of hierarchical organization

Nodes at a high level in a hierarchy may give the appearance of being very “smart”

This appearance is a consequence of their position — at top of hierarchy

As the top node in a hierarchy, a node has the processing power of the whole hierarchy• Compare:

The general of an army The head of a business organization

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Perception of height – Experiment by P. R. Wilson (1968)

Subjects were students in an Australian university• Five separate classes• A man was introduced as a visitor from Cambridge Univ.

① Class 1: introduced as a student② Class 2: introduced as a demonstrator③ Class 3: introduced as a lecturer④ Class 4: introduced as a senior lecturer⑤ Class 5: introduced as a professor

• The man then left the room• Students were asked to estimate his height• Height estimates increased avg. ½ inch for each step• “Professor” was estimated to be 2 ½ inches taller than

“student”64

Perception: We see what we expect to see

• Top-down effects in thinking and perception• The mechanism: bidirectional connections• Conceptual structure influences perceptual operations• Higher-levels of perceptual structure can likewise

influence lower levels• We see what we expect to see

Where do the expectations come from? Ans: From information already present in our

conceptual/perceptual systems• Thus to a large extent we see only the past

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T h a t ‘ s i t f o r t o d a y !

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