Overview of Topics

Localization ?

Several common Errors

LOCALIZATION OF FUNCTION

Unitary view

Several common Errors

Is There Localization of Function?

It is accepted as axiomatic -- to understand brain function one must establish the structural boundaries of the neuron aggregates acting as functional units in behavior.

It is an inexact out-moded formulation employed for convenience.

Regional localizationists

View the unitary view proponents as ignoring the fine structure of the brain and not dealing with the appropriate problems.

Unitary view

They hold that complex behaviors are not simply the result of compartmentalized functions in specific structures linked by long fiber tracts.

They view focal lesion studies as yeilding too much to the temptation to reduce complex functions (i.e.) memory to simpler elements that can be explored more conveniently.

Believe that complex processes are not simply the sum of the components.

General

Difficult to define the border between complex behavior and integrated, but relatively simple, reaction patterns.

Few quantitative studies have been conducted on human subjects.

Other problems:

a. remote effects of fiber tract interruption
b. alterations in blood supply
c. influence of seizures
d. presence of additional recognized or unknown lesions
e. other disease processes
f. effects of damage to overlying & adjacent structures
g. effects of age
h. environmental factors (stress).

Several common Errors

1. It may be erroneously assumed that impairment is limited to specific feature when many other features of complex behavior also impaired.

2. It may be erroneously assumed that afferent, motor, autonomic & speech functions are not disturbed, when alterations at this level are interfering with complex behavior & with assessment methods.

3. It may be erroneously assumed that the region of dysfunction is limited to a circumscribed region of widespread damage but may be due to less conspicuous in another area.

4. It may be erroneously assumed that electrical stimulation has focal effect.

5. It may be erroneously assumed that behavior is altered by a lesion without condiseration of effects of lesions of equivalent mass elsewhere.

6. It may be erroneously assumed that quantitative or qualitative differences in complex behavior stem specifically from the site or side of the lesion when they are the consequence of the size of the lesion.

7. In intact animals, learning skilled motor acts with one limb could be performed by contralateral limb.


a. Problem with Behavioral Terminology
b. Problem with Methodology
c. Problem with Design
d. Individual Differences
e. Hierarchical System

Hypotheses for Revised View

1. Complex brains evolved from less complex

2. New Neural systems were connected with old and interacted or controlled.

3. Increasingly complex behaviors first evolved from interaction of areas

4. As cortex evolved interactions increased for different functions allowing some cognitive processing to occur without direct ties to lower systems

5. Recovery of Function

LOCALIZATION OF FUNCTION

Is There Localization of Function?

Chapman, L.F., & Wolff, H.G., 1961, The human brain - one organ or many? Archives of Neurology, 17-25.

It is accepted as axiomatic -- to understand brain function one must establish the structural boundaries of the neuron aggregates acting as functional units in behavior.

Researchers strive to place lesions so that a single defined aspect of behavior & no other is impaired by a lesion in one precise site & no other.

This is a traditional view which predated Galen, was supported by Gall and Broca, and Fritsch & Hitzig's studies.

This view directs much of the research even though the naive formulations of phrenologists and anatomical parcellation of cytoarchitectonics are rejected by almost all.

It is an inexact out-moded formulation employed for convenience.

During the 100 yrs since Broca, relatively predictable relationships have been established between circumscribed sites in the brain and certain aspects of sensation, movement, speech, sleeping, waking, etc.,

But what of more complex aspects of behavior? Things such as learning, memory, mood, attitudes, etc.

Alternative concept holds the unitary view that each of the various categories of complex behavior implicates the activity of much, if not all, of the brain.

Study of specific behaviors yeilds observations about elements and not about complex behavior itself.

When functions are expressed at a simple level, there is a degree of regional specialization at all brain levels with exception of association cortex.

The unitary view would suggest that a loss of a portion of the brain would result not in the abolition of a specific category of complex behavior,, but in a graduated deterioration of many features of complex behavior, in proportion to the mass of the lesion & regardless of site (mass-action).

1. This view will have to be modified to account for more simple levels of function (neocortex, specifically association cortex).

2. In motor, sensory, and lower systems, the principle of mass-action is of trivial significance.

Regional localizationists

View the unitary view proponents as ignoring the fine structure of the brain and not dealing with the appropriate problems.

Some believe that a brain behavior relationship will be definitively established when satisfactory behavioral assay procedures are developed and suitable patients are studied.

They find the regional localization view attractive since it offers the opportunity to employ new anatomical and electrophysiological methods to attack the problem.

Furthermore it is a natural extension of procedures that have worked on more simple systems.

They view data supporting mass-action as an artifact of behavioral assay methods (data by these methods depends upon a large number of elements, each related to a specific locus.

Unitary view

Four categories of higher integrative function was defined.

1. capacity to express needs, appetites, and drives
2. capacity to integrate the mechanisms for goal achievement
3. capacity to initiate, organize & maintain appropriate adaptive and defensive reactions.
4. capacity to maintain organization during stress & recover promptly.

Impairment is less with higher premorbid functioning.

Loss of higher integrative functions related to the size of the lesion regardless of the site.

Impatient with investigations which only evaluate behavioral changes related to specific sites.

They wish to attack more complex behaviors.

They hold that complex behaviors are not simply the result of compartmentalized functions in specific structures linked by long fiber tracts.

They view focal lesion studies as yielding too much to the temptation to reduce complex functions (i.e.) memory to simpler elements that can be explored more conveniently.

Believe that complex processes are not simply the sum of the components.

General

Difficult to define the border between complex behavior and integrated, but relatively simple, reaction patterns.

Few quantitative studies have been conducted on human subjects.

Other problems:

a. remote effects of fiber tract interruption
b. alterations in blood supply
c. influence of seizures
d. presence of additional recognized or unknown lesions
e. other disease processes
f. effects of damage to overlying & adjacent structures
g. effects of age
h. environmental factors (stress).

Example of Memory

1. Memory disturbance linked to specific areas of damage.

2. severe alcoholism - medial temporal & periventricular lesions.

3. Memory impairment noted after temporal lobe lesions.

Several common Errors

1. It may be erroneously assumed that impairment is limited to specific feature when many other features of complex behavior also impaired.

a. Intelligence - may not be impaired with 120 grams of tissue removed (1/10 of total brain mass).
b. Emphasis on IQ & mental defects as sole evidence is inadequate.
c. Such defects may occur only after massive lesions.
d. preservation of IQ can give false impression that faculties other than the one noted are intact.

2. It may be erroneously assumed that afferent, motor, autonomic & speech functions are not disturbed, when alterations at this level are interfering with complex behavior & with assessment methods.


a. Almost all assessment of humans relies on speech.
b. ANS changes way be undetected yet impair complex behavior

3. It may be erroneously assumed that the region of dysfunction is limited to a circumscribed region of widespread damage but may be due to less conspicuous in another area.


a. boundary definition is problem with atrophy, TBI, vascular disease.
b. During life these boundaries are unknown.
c. Most conspicuous lesion may not relate to specific behavior studied
d. Diseased but viable neurons may be as disruptive as absent cells.
e. Wide variation if dysfunction before surgical intervention.
f. Reduced anxiety, aggression etc may interact with loss of function.

4. It may be erroneously assumed that electrical stimulation has focal effect.


a. Obviously influences remote neurons.

5. It may be erroneously assumed that behavior is altered by a lesion without consideration of effects of lesions of equivalent mass elsewhere.

6. It may be erroneously assumed that quantitative or qualitative differences in complex behavior stem specifically from the site or side of the lesion when they are the consequence of the size of the lesion.


a. Frontal lesions are larger at detection
b. Right side lesions are larger than left.

7. In intact animals, learning skilled motor acts with one limb could be performed by contralateral limb.

a. If corpus callosum and anterior commisure were first sectioned, this transfer did not occur.
b. Albert's research found same thing.
c. Indicates that both hemispheres are implicated in learning & memory even though performance is restricted to one region.

8. Unitary view not popular.

9. The brain is both one organ and many.

10. Areas or centers for primary processing?


a. Phrenology
b. Blindly looking for localization of function
c. Knowledge based on false assumptions
d. Functions not localized in the brain

(1) Lashley (search for engram) - not in brain.

2. Problem with Behavioral Terminology

a. Logical constructs
b. Subdivide into specifics to study
c. Appears unlikely that component parts equal total

3. Problem with Methodology

a. Stimulation - generalized - voltage specific
b. Lesion - pressure, tract disruption
c. Recording - generalized or time locked
d. biochemical - generalized

4. Problem with Design


a. Ho: may be incorrect ( try to refute)
b. Easy to refute other's Ho's

5. Individual Differences


a. General lack of interest
b. Major importance in man
c. May be due to size of anatomical structures (Geschwind)

6. Hierarchical System


a. BS - LS - Cortex
b. Multiple representations

(1) Geschwind - shift down with lesions
(2) Cortical connections serve to bypass linearity

Hypotheses for Revised View

1. Complex brains evolved from less complex

a. C J Herrick

2. New Neural systems were connected with old and interacted or controlled.


a. Multiple representation of different functions.
b. H. Jackson hierarchy
c. P. Florens & C. Lashley

3. Increasingly complex behaviors first evolved from interaction of areas


a. In some cases the interconnected areas have similar functions.
b. In others, the functions are quite different but are related to the complex behavior.

4. As cortex evolved interactions increased for different functions allowing some cognitive processing to occur without direct ties to lower systems


a. Geschwind - Angular Gyrus.

5. Recovery of Function


a. The price for recovery of function is generalized decline in cognitive function.
b. Accuracy of localization of functions, thus, declines with time.
c. Multiple representation present

(1) Recovery involves shift to lower area
(2) Or shift to alternate pathways
(3) Suppression appears to come from secondary themselves