self and medical science part 2

[Guest guest]

[continued from part 1]

 

Studies of human patients reflect the

multidimensionality of self-representation by showing

that particular functions can be spared when others

are impaired. For example, a subclass of amnesic

subjects with bilateral lesions in the hippocampal and

associated cortical structures are unable to acquire

new knowledge and have lost essentially all

autobiographical information. For example, the patient

R.B. lives essentially within a moving 40-s time bin

(3). Although R.B. does suffer diminished

self-understanding, he nevertheless retains many

elements of normal self capacities, including

self-control in social situations and the fluent and

correct use of "I." He also knows his current body

configuration and status, and he can engage in

self-imagery, identify feelings such as happiness, and

show sympathy with the distress of others. The

existence of such amnesics is a counterexample to the

seemingly obvious hypothesis that one's self is

constituted by personal narrative (9).

 

Schizophrenia, known to involve decreased prefrontal

activity and increased striatal activity (23),

presents a different dimension of self-dysfunction.

During a florid episode, a schizophrenic may have good

autobiographical memory, but suffer deep confusion

about self/nonself boundaries, e.g., responding to a

tactile stimulus by claiming that the sensation

belongs to someone else or that it exists somewhere

outside of him. Auditory hallucinations, often

considered diagnostic of schizophrenia, exemplify

integrative failure. The "voices" appear to be the

patients' own thoughts or inner speech, but they are

not represented, and thus not recognized, as such (24,

25). The anesthetic ketamine and drugs such as LSD can

trigger similar phenomena.

 

A patient with lesions in right parietal cortex,

resulting in loss of sensation and movement on the

left side of the body, may firmly deny that her left

limbs are in fact hers. On occasion, a patient with

limb denial will use the normal right arm to try to

throw the paralyzed left leg out of the bed, insisting

it is alien. Despite suffering compromised

body-representation, the patients may nevertheless

have normal autobiographical memory as well as other

self-representational functions such as knowing

whether they feel bored or hungry. Patients with

lesions in the anterior cingulate region may exhibit

alien hand syndrome. In these cases, the

contralesional hand will sometimes behave as though it

is independently controlled. Patients with alien hand

syndrome sometimes control their embarrassing alien

hand with verbal commands.

 

Self-regulating functions can also be selectively

impaired. Lesions in prefrontal cortex, especially in

the ventromedial region, have been followed by

significant changes in self-control, and particularly

in the capacity to inhibit unwise impulses, despite

normal functioning of many other self-representational

capacities. Personality changes commonly occur with

prefrontal damage. Hitherto quiet and self-controlled,

a person with lesions in the ventromedial region of

frontal cortex is apt to be more reckless in

decision-making, impaired in impulse control, and

socially insensitive (3, 17, 18).

 

 

Evolution of Self-Representational Capacities

The most fundamental of the self-representational

capacities probably arose as evolution stumbled on

solutions for coordinating inner-body signals to

generate survival-appropriate inner regulation. The

basic coordination problems for all animals derive

from the problem of what to do next. Pain signals

should be coordinated with withdrawal, not with

approach. Thirst signals should be coordinated with

water-seeking, not with fleeing, unless a present

threat takes higher priority. Homeostatic functions

and the ability to switch between the different

internal configuration for fight and flight from that

needed for rest and digest require coordinated control

of heart, lungs, viscera, liver, and adrenal medulla.

Body-state signals have to be integrated, options

evaluated, and choices made, since the organism needs

to act as a coherent whole, not as a group of

independent systems with competing interests.

 

The Neural Platform

The most basic level of inner coordination and

regulation occurs in the brainstem, anchoring what

Damasio refers to as "the protoself" (12). In

vertebrates, the brainstem-hypothalamic axis is the

site of convergence of signals from the viscera,

internal milieu, and the somatic sensory system. Also

located in the brainstem are nuclei that regulate

vital functions, sleep-wakefulness cycles, arousal,

attention, and the emotions. This level of

integration, shared across many species, is the

nonconscious neurobiological platform for higher

levels of self-representation.

Other, more complicated and flexible aspects of the

self demand greater computational resources. Wolpert

(26) and Grush (27) have proposed that increased

accuracy in planning and execution of movement in

space-time is achieved by cortical models of the body

in relation to its environment. Roughly, a somewhat

sloppy inverse model is connected to an

error-predicting forward model, and the two converge

on a good answer to the problem of how to move a

many-limbed body in just the right way at just the

right time.

 

If, for example, the goal is to reach a plum, the

inverse model gives a first-pass answer to this

question: What motor command should be issued to get

my arm to contact the plum? Taking the

command-proposal, the forward model calculates the

error by running the command on a neuronal emulator,

and the inverse model responds to the error signal

with an upgraded command. Emulation is faster and

safer than real-world feedback. Assuming the forward

and inverse models are also capable of learning, this

organization can be very efficient in acquiring a wide

range of sensorimotor skills. With sufficient access

to background knowledge, goal priorities, and current

sensory information, emulators can compute accurate

solutions to complex motor problems.

 

Rudimentary neuronal emulators, grounded in the basic

coordinating and self-regulating functions, can in

turn be upgraded to yield fancier inner models of

planning. Emulators can facilitate making an

appropriate movement after the target has become

invisible, perhaps because the prey is in a cavity or

the predator is sneaking up on the prey. More

generally, with appropriate connectivity, an emulator

could run off-line to plan for the long-term future,

thus deploying extended body-image manipulation.

Additional modification permits off-line emulation of

cognitive states. For example, when planning the

details of a raid, one may imagine oneself feeling

anxiety while stalking the enemy camp, assessing the

attentiveness of the camp guards, formulating specific

intentions to outfox wary guards, and so on. Like

body-image manipulation used in planning a climb, this

is mind-image manipulation used in planning a complex,

extended me-them encounter (27).

 

 

Consciousness and Self-Representation

An appealing hypothesis defended by Damasio (12) is

that the self/nonself distinction, though originally

designed to support coherencing, is ultimately

responsible for consciousness. According to this view,

a brain whose wiring enables it to distinguish between

inner-world representations and outer-world

representations and to build a meta-representational

model of the relation between outer and inner entities

is a brain enjoying some degree of consciousness.

Thus, such a system could represent the relation

between the thistle and itself as "that (outer) thing

causes me (inner) pain." Conceivably, as wiring

modifications enable increasingly sophisticated

simulation and deliberation, the self-representational

apparatus becomes correspondingly more elaborate, and

therewith the self/not-self apparatus. On this

hypothesis, the degrees or levels of conscious

awareness are upgraded in tandem with the

self-representational upgrades. Thus, chimpanzees, but

not frogs, know whether they can be seen by a

subordinate female but not the dominant male. Infant

human development studies and nonhuman primate studies

support these hypotheses (28, 29).

Whether neuroscience can build on these foundations to

discover full and detailed explanations of all

self-representational phenomena remains to be seen.

Still, unpredictability obscures the destiny of

essentially all neurobiological puzzles, including

noncognitive functions such as thermoregulation. An

abiding challenge in neuroscience is to discover the

basic principles governing the integration of

information at various levels of brain organization

and at various time scales. This challenge is not

confined to the neuroscience of self-representation,

but confronts neuroscience generally.

 

 

One can only imagine what a leap of faith it is for a

"thinking person of science" not familiar with Ma

Shruti to accept his or her "self" as the very

substratum of the universe!

 

A thousand pranams to Mother Shruti.

 

Hari OM

Shyam