Fractures and Bindings of Consciousness

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Oct 20, 2013 (3 years and 11 months ago)

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?


FEATURE ARTICLE

Fractures and Bindings of Consciousness

Observing how awareness breaks down in epileptic seizures provides clues to its normal workings in
the brain

Don M. Tucker
,

Mark D. Holmes

Amer Sci 2011 Jan
-
Feb


?
Every second, our brains take feedback
from the world and provide us with a sense of
consciousness: awareness of wh
at we are doing and
what we have just done. How this process works in the
brain is no simple matter. But sometimes examining
how a process fails

as consciousness does in people
afflicted with epilepsy

enlightens us to how it works.
With recent advances in
mapping the spread of epileptic
seizures, we can now align the unique fractures in
consciousness that occur during seizures with the interference that seizures cause
in specific cerebral networks.


Loss of ongoing memory, which disrupts the continuity of
consciousness, occurs
when seizures spread through the brain’s corticolimbic networks. The fractures in
consciousness that occur in these

limbic seizures

suggest that one component of
consciousness is provided by
ongoing memory
, which allows us to use the
knowledge of the immediate past and anticipate the immediate future. This
component of consciousness is necessary for the mind’s continuity in time.

Volitional control of consciousness is disrupted in

absence spells
, in which a
seizure spreads through fron
tothalamic circuits.
The disruption of mental capacity in
absence spells suggests that an integral component of consciousness is the
voluntary control of intentions.

This component is closely related to, but separable
from,
selective attention
, in which so
me contents of consciousness are
“spotlighted” while others fade to the background. The control of intentionality
allows consciousness to coordinate mental resources and to provide the sense of
one’s active role in personal experiences.


Finding Consciousn
ess

A classic debate in brain research has been that
b
etween

localization

and

mass action
.

The question is whether psychological
functions, such as spatial memory and verbal reasoning, are localized in specific
brain regions, or whether they emerge from the mass action of the brain as a
whole. With modern evidence on localized brain activity, a
s seen by neuroimaging
methods such as
functional magnetic resonance imaging (fMRI) or dense
-
array electroencephalography (dEEG)
,
it may seem that localization clearly has
won out. Indeed, localized brain activity can be reliably demonstrated with many
cog
nitive tasks.


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However, the best scientific understanding we have of how psychological function
could arise from human neural networks has come from artificial neural
-

network
models in computational neuroscience.

These models illustrate principles of
dist
ributed
-
information representation that are very similar to the classical
notion of mass action.

A primary principle, sometimes called

connectionism
,

is
that
information is represented in the patterns of connections between neurons, not
in the neurons
themselves.

Connectionist simulations show brainlike properties that
have never been possible to create with traditional artificial intelligence. One
example is content
-
addressable memory. With a conventional computer, you must
specify not only what is to
be stored in memory but the “address” where it is to be
placed. But when information is represented in the patterns of connections in a
network, then simply presenting the network with the content (such as the pattern
of a face to be recognized) causes it
to address that memory as an intrinsic feature
of the activation of the widespread distributed connections.

Informed by principles of distributed computation, neuropsychological theorists
have generated new concepts for relating complex qualities of the hu
man mind to
the specific properties of cerebral networks. For example, Giulio
Tononi

at the
University of Wisconsin and
Christoph Koch

at the California Institute of
Technology have drawn upon connectionist reasoning as they interpret evidence
suggesting h
ow consciousness might arise within the large
-
scale networks of the
cerebral hemispheres. Although the study of anatomy shows that there are
extensive neural connections within and between the cerebral hemispheres that
could be active, Tononi and Koch theo
rize that consciousness emerges from the
dynamic pattern of physiological connections that are active at any one point in
time as an integrated assembly.

The idea of memories stored in the patterns of connections among neurons
was first formulated by Sigmu
nd Freud in the 1890s.

The issue was
addressed by mathematical formulations of nerve
-
net cybernetics by
Warren
McCulloch and Walter Pitts
at the University of Chicago in the 1940s. This issue
remains important to modern neuroscience theories such as that p
roposed by
Tononi and Koch. From the connectionist perspective, if we could understand the
control of large
-
scale physiological assemblies in the brain, we could also
understand the control systems necessary for regulating consciousness.

All of this inform
ation leads back to
epilepsy
, because a dramatic clue to the
sensitization and spread of physiological network assemblies may be found in the
pathological phenomena of seizures.
The ways that seizures engage certain
networks and not others may show how dyn
amic ensembles of neurons
can be formed within specific anatomical networks.

The psychological deficits
that are characteristic of these specific seizures may then provide clues to the
normal separation of the functional components of consciousness.





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A
Nested Framework

?
A first principle of
neuropsychological function is basic enough tha
t it
is easily overlooked.
The human brain’s
psychological operations are organized in
relation to its general architecture, which
comprises a nested hierarchy of the evolved
structures

of the vertebrate brain. This hierarchy
can be described as a vertical

dimension of neural
organization: More recently evolved structures are stacked on top of more primitive
ones

(see Figure 2).

As seen most clearly in the still
-
forming brain of the human
fetus, the cortex is dependent on the major circuitry of the
subcortical
telencephalon, including the limbic circuits and those of the basal ganglia. These
telencephalic (end brain) systems are in turn dependent on regulatory influences
from the thalamic and hypothalamic divisions of the diencephalon (interbrain),
w
hich sits on top of the brain stem and provides a gate for the traffic into and out
of the telencephalon. The functions of the diencephalon are in turn dependent on
ongoing support from the brain stem’s mesencephalic, metencephalic and
myelencephalic level
s of organization, regulating primitive but essential functions
such as breathing, heartbeat and the brain’s level of arousal.

?
Some people with epilepsy
experience generalized

tonic
-
clonic seizures,

or
convulsions. Convulsions are the most
severe form of an epileptic seizure and tend
to “generalize” or spread throughout the
brain’s
vertical organization.

As they do, these
seizures provide a clear demonstration of the
brain’s vertically organized architecture, through
which more recently evolved networks are
embedded within the control mechanisms of more
primitive networks. To the ext
ent that multiple
vertical levels of the brain’s control systems are
involved in major changes in consciousness, such
as in sleep and dreams, we can see that these
nested control systems of the brain must be continually integrated to shape
qualities of eve
ryday experience.

?
More specific clues are given by seizures that
remain limited to
specific circuits in the forebrain (the
diencephalon and telencephalon). Seizures that do not spread
are described as localization
-
related or partial seizures. If they
impair consciousness, they are termed

complex partial
seizures
.

A common feature of thes
e seizures is that they
engage the limbic networks at the medial core of the cerebral
hemisphere. The limbic networks are centered on the medial
temporal lobe, so when epilepsy involves partial seizures, it is
often referred to as temporal
-
lobe epilepsy
. I
t is the

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most common form of epilepsy in adults. In patients with recurring temporal
-
lobe
seizures that are poorly controlled by antiepileptic drugs, neurosurgical removal of
the epileptic tissue may be necessary. In that case, localizing the onset of the
seizure discharge is necessary to guide the neurosurgical procedure. It is critical to
determine that the patient’s seizures stem from one temporal lobe, and only that
temporal lobe, if the limbic tissue of that lobe is to be removed. With recent
advances
in dEEG technology, sampling the brain’s electrical field can be
accomplished with electrodes that cover the head fully. With adequate coverage,
the electrical measurements can then be registered with a three
-
dimensional MRI of
the person’s head tissues. T
hen computer visualization can extract the cortical
surface and build a detailed electrical model of the person’s brain. With this precise
electrical model and dense
-
array measurement, the onset of seizure activity can be
estimated from the noninvasive dEE
G at the head surface. Validation studies with
intracranial electrodes, placed directly on the brain surface, have provided evidence
that the dEEG estimate of seizure onset is sufficiently accurate to guide
neurosurgery.

Limbic Central

Clinically,
epileptologists and neurosurgeons have considerable evidence showing
that when seizures appear to begin in the temporal lobe, they are starting in the
limbic networks of the medial temporal lobe. To understand why limbic networks
tend to generate seizures,

researchers have conducted experimental studies of
induced seizures in animals. This research has suggested that the reactivity of
limbic networks in epilepsy reflects the high level of electrophysiological, and
perhaps functional, excitability of limbic
tissue.

?
The limbic networks are in a good
position to be reactive to events anywhere
in the
hemisphere because they are centrally located.

The last
several decades of neuroscience research have yielded
important insights into the connectional architecture of the
cerebral hemispheres, and a key finding has been the central
role of limbic ne
tworks. Research by
Deepak Pandya

and his
colleagues at Boston University has introduced quantitative
methods to studying the connectivity of the primate cortex. In the earlier
qualitative studies, any neural connection between one area of cortex and anoth
er
was sufficient to consider them connected, leading to complex, rather
indiscriminate maps that implied that most areas of cortex were interconnected to
each other. Instead, the quantitative studies showed that
the primary paths of
neural connections lin
k the sensory and motor cortices with their bases in
limbic cortex.

Moreover, the density of interregional connections (for example,
connecting auditory with visual association areas) becomes greater closer to the
limbic system. The implication of this con
nectional anatomy is that the limbic
regions are the primary integrative networks of the hemisphere, whether for
sensory integration in the posterior brain or for motor organization in the anterior
brain. The architecture implied by this evidence is remark
able. It shows how the
classic “association” areas of the cortex are actually intermediate, falling between
primary sensory or motor areas and their limbic base. This architecture can also
help explain why seizures tend to engage limbic regions: These regi
ons are at the
core of the hemisphere’s connectivity.


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The functional significance of the hemisphere’s connectional architecture is clearly
illustrated by the role of corticolimbic interaction in forming memories. This activity
results from the interaction
between the neocortical networks, for example, those
handling sensory or motor functions, and the limbic networks at the core of the
hemisphere. Evidence from both human clinical studies and animal experiments has
shown that if the connections between neoc
ortex (for example, auditory cortex)
and limbic cortex are severed, the relevant memories (for example, memories of
sounds) cannot be formed. Previous memories may be recalled (depending on the
severity of the brain lesion), but new ones cannot be created.

This evidence has
two important implications. First, memories are not localized in one spot in the
hemisphere but are distributed across multiple networks, including limbic,
association cortex and primary (for example, auditory) cortex. Second, in order t
o
form a memory, some physiological process, often called consolidation, is necessary
to allow the perception of an event to engage responses in limbic cortex. These
responses then feed back (in some way not yet understood) to energize the
memory trace, wh
ich is not discretely localized but, rather, distributed across the
linked corticolimbic networks.

Binding of Ongoing Memory

The limbic networks, linked closely to the body’s homeostatic, visceral regulatory
mechanisms in the hypothalamus, are responsible
for motivational control.
Considering this, a reasonable hypothesis is that the functional role of limbic
networks in memory consolidation is to regulate the memory process to ensure that
motivationally significant experiences are provided with adequate co
nsolidation to
be retained in memory. Remarkably, the same excitability of limbic circuits that
causes them to resonate to motivationally significant experiences may lead them to
be seizure
-
prone.

?
We have seen that human epilepsy often
involves the temporal
-
limbic networks; some researchers
have hypothesized that the recurrent seizures of
epilepsy may
progress toward temporal involvement wherever they
originate in the cortex. In a phenomenon
called

kindling,

seizure discharges in experimental animals are
first started in an area of neocortex through repetitive
electrical stimulation. The fi
rst stimulation causes only a direct
local discharge, but subsequent stimulations cause a kindling
or exaggeration of the response, leading to continuing,
seizurelike discharges. The researchers using this method
soon found that wherever the kindling was s
tarted, the
seizure discharges tended to progress to the limbic core of the hemisphere. The
close association between kindling and learning was discovered in an experiment a
number of years ago by the team of Jerri Janowsky at Oregon Health Sciences
Univer
sity. The team found that seizures, once kindled in an animal’s brain, could
be conditioned or learned through association with a sensory stimulus, such as a
sound. The limbic resonance that recruits the electrophysiological excitement of a
seizure appears

similar if not identical to that which recruits the consolidation of a
significant event in memory.


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If limbic seizures impinge on the anatomy of memory, what happens to a person’s
memory after a seizure? Typically, the person shows retrograde amnesia, mea
ning
the loss of memory extends gradually back in time for minutes or even hours
before the seizure. Because of this recent memory loss, the person is disoriented
and unable to act coherently. The person has no ongoing memory of his or her
location or what

has been happening. This is a clue to the normal coherence of
consciousness in time.

?
Given the critical role of temporal and limbic
networks in memory, seizures that affect these networks most
strongly may be expected to cause severe impairment of
recent memory. Observations by Dan Drane of the
University
of Washington’s Regional Epilepsy Center have suggested that
temporal
-
lobe seizures may indeed affect recent memory
more than other seizure types.

We think that the disorder of recent memory that accompanies limbic seizures
provides an important

clue to the neurophysiology of a key aspect of
consciousness: ongoing memory
. Without the continuity of recent memory, and the
associated ability to anticipate the immediate future, the temporal span of
consciousness becomes vanishingly thin. Imagine that

you have no memory of
what happened one second ago. Are you still conscious? Certainly you are
conscious of this one second, and you could argue that immediate consciousness is
preserved. Yet even a moment’s reflection makes it clear that there must be so
me
historical scope of awareness

and without it, functional consciousness retracts
toward a complete loss of meaning.

Recognizing that limbic memory mechanisms are the basis of the frontal lobe’s
ability to plan for future actions, the late Swedish neurosc
ientist
David Ingvar

described planning as “memories of the future.” Similarly, acknowledging the limbic
base of the cerebral hemisphere’s functional architecture, American biologist Gerard
Edelman

described consciousness as “the remembered present.” Consi
dering how
normal consciousness requires both the context of recent memory and the
projection of events into the unfolding future, we suggest that ongoing memory is
an essential component of human consciousness. As shown by various disorders of
consciousne
ss, including not only limbic seizures but delirium and dementia, the
loss of ongoing memory is devastating for the conscious control of cognition. As
recent memory shrinks, so does conscious anticipation of the future. Ongoing
memory allows us to orient t
o person, place and time. In normal consciousness, we
continually project the active residuals of immediate history into the unfolding
future, thereby maintaining the temporal continuity of mind.

Careful analysis of the effects of limbic seizures thus prov
ides a novel insight into
neuropsychological activity that binds the mechanisms of consciousness in time.
This insight can be refined further by contrasting limbic seizures with a disorder of
consciousness caused by a kind of seizure that specifically does

not impair ongoing
memory.





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Absence Spells

?
Although they may continue into adulthood,
absence seizures typically affect children. There is a
momentary disruption of consciousness, during whic
h the
person is unresponsive and unable to carry out voluntary
actions. However, unlike the loss of consciousness from any
other neural disruption

such as fainting, drug toxicity or
concussion

the person does not fall down, appears to be
alert and does not

become disoriented. During the seizure,
the brain emits large spike
-
wave discharges that suggest a
generalized seizure. However, immediately after this typically
brief seizure, the person may continue the previous activity or
pick up the conversation wher
e it left off, showing that he or
she remains fully oriented in time.

The absence spell is thus a remarkably
specific

lesion,

or disruption, of consciousness, and it is
particularly remarkable in what it does not cause:
disruption of ongoing memory.

Consistent with this
specific psychological effect, the anatomy of absence epilepsy
provides clues to a specific circuitry of the thalamus and frontal lobe. The
implication is that this neural circuitry must be integral to the voluntary control of
thought

and action in the normal brain.


Several lines of evidence suggest that abnormal discharges from the thalamus
figure in the development of spike
-
wave seizures in animals, and in similar
discharges in absence epilepsy. The thalamus can be described as the
gateway to
the cerebral cortex, binding the networks for specific mental functions.
With the
exception of the sense of smell, all sensory and motor pathways enter or
exit the cortex through thalamic relays, and the thalamus is capable of
blocking transmiss
ion in these relays
. A unique feature of the thalamus, the
thalamic reticular nucleus (TRN)
, is a thin sheet of neurons surrounding most of
the thalamus. This network provides direct inhibitory control over the
thalamocortical relays. Importantly, as anoth
er example of the complexity of the
brain’s self
-
regulatory systems, the TRN is itself under cortical control, from specific
networks in orbital and frontopolar cortex.

This evidence of a localized, frontal
-
lobe control network for regulating thalamic
mech
anisms has proven important in interpreting localized seizure activity in
absence spells. In our dEEG studies of the pathological discharges during these
spells, we found that, even though these discharges were thought to cover large
areas, the spikes are
highly localized. Indeed, they are specifically localized to the
orbital and frontopolar networks of the frontal lobe, which are in turn critical to
regulating the thalamus. The implication of this new evidence is that the seizure
discharge reflects some a
bnormality in the physiological activity in the frontal
networks that then cascades in a pathological loop through the frontothalamic
circuitry. The cortical discharge appears to affect the TRN and thalamus, and
thereby disrupts the thalamic control of the

cortex itself, perhaps leading to the
next cascade of spike
-
wave discharge. Does this evidence of pathological function
provide clues to the normal, adaptive functions of the frontothalamic circuitry? The

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evidence is complex, because it suggests even grea
ter specificity in separating the
circuits controlling attention

(the application of mental resources to certain
events or topics) from
intention (the current goal of mental activity).


Patterning the Spotlight

The specificity of the frontal lobe’s control

over thalamocortical mechanisms of
attention has been demonstrated by recent anatomical evidence gathered by Basilis
Zikopoulos and Helen Barbas at Boston University. These data show how specific
networks in the frontal lobe project to specific regions of

the TRN, and thereby to
specific thalamic nuclei. The relevance to controlling attention is shown by the
pathways from certain frontal networks (on the lateral surface) that project to the
regions of the TRN that control the specific sensory nuclei of the

thalamus. These
circuits are well suited to
controlling the “spotlight” of attention by allowing
the thalamus to highlight certain sensory data while pushing other input to
the background.

Importantly, however, the seizure discharges during an absence spe
ll do not seem
to engage the frontal networks that regulate the spotlight of attention. Rather, in
our dEEG studies we found that the spikes of spike
-
wave absence discharges
engage the medial frontal poles; these are the networks that Zikopolous and
Barbas

found to be connected to the rostral pole of the TRN, which in turn projects
to the anterior nuclei of the thalamus, also called the limbic thalamus. This
frontothalamic circuit, rather than controlling the spotlight, appears to integrate
limbic contribut
ions to the state of arousal and motivation. One interesting line of
animal research suggests that activity in this circuit is related to the animal’s
head
orientation,

apparently tracking the self
-
centered locus of the animal’s current
intentions.

Conside
ring this specific functional circuitry in the seizures that cause
absence spells, we think that the loss of conscious control of behavior in
this disorder reflects an impairment of a frontothalamic circuit that is
integral to the voluntary control of inte
ntion.

This is not the selective attention
to one sensory focus, but the maintenance of the alert intentional state that allows
cognition and behavior to pursue a motivated goal. Absence seizures thus disrupt a
specific component of consciousness, the pers
on’s current intention that then binds
multiple other component mental operations within a coherent, goal
-
oriented
episode of experience.

Even as voluntary intention is disrupted in the absence spell, ongoing memory
remains relatively intact. This implies
a fractionation of consciousness by different
seizure types. Limbic seizures impair ongoing memory over a considerable interval
of time, so that even as consciousness is regained it is incomplete and disoriented.
Absence seizures create a more focal disrup
tion of consciousness, impairing
voluntary intentional action but not degrading the continuity of ongoing memory.
With ongoing memory more or less intact, the person retains the subjective
orientation to the immediate experiential context, and can therefor
e pick up the
conversation where it left off. By fractionating consciousness in a specific way,
absence seizures show the specificity of both what is lost (voluntary intention) and
what is retained (ongoing memory and orientation).


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Dynamic Consciousness

Th
e unique fractures in consciousness that occur in seizure disorders may offer
clues to the underlying mechanisms that bind consciousness within the large
-
scale
networks of the cortex. Ongoing awareness of the context appears to require the
operation of cor
ticolimbic networks. Interestingly, this contextual awareness is
needed to meet the clinical test of mental competence. To provide a quick
assessment of impaired consciousness when a patient appears confused, physicians
and psychologists use the test of “o
rientation times three.” This tests orientation to
person (“What is your name?”), place (“Can you tell me where you are?”) and time
(“What is the date today?” “What month is it?” “Do you know who the U.S.
President is now?”). Consciousness may be clouded t
emporarily by delirium or
disorganized permanently by dementia. In contrast, volitional control of
consciousness seems to require frontothalamic circuits, both for the selection of
focused processing, such as in selective attention, and for the regulation
of the
more general state of purposeful intention, which is impaired during the absence
spell.

Thus both corticolimbic and frontothalamic mechanisms appear necessary
for normal consciousness. They seem to bind patterns of physiological
coherence within cer
ebral networks
. And certainly this is only part of the story
of the brain’s physiological assemblies: These patterns of network coherence must
be organized within the general pattern of vertical integration, drawing on support
from brain stem projection sy
stems that regulate cerebral arousal.


Consciousness as a Phenomenon

It probably makes sense to most people to consider consciousness as a unitary
phenomenon, an indivisible quality of subjectivity. Yet the fracturing of
consciousness in absence seizures i
s particularly impressive evidence for the
hypothesis that some aspects of explicit voluntary control, mediated by
frontothalamic circuits, can be separated from the continuity of ongoing memory.
When we employ reasoning from anatomy and the specificity of

absence
discharges, even finer distinctions can be made, implying that the selection of the
focus or spotlight of attention is separable from the voluntary control of the
intentional state itself. Now that we can separate them through neurophysiological
a
nalysis, can we recognize these components of consciousness in subjective
experience?

From a clinical perspective, understanding the specific neural mechanisms of
seizure patterns may lead to better diagnosis and more focused therapies, whether
drug
-
based
or surgical. If we succeed in understanding the fractures in
consciousness caused by specific seizures, then we may also gain a better
appreciation of the psychological challenges faced by our patients with seizure
disorders.

From a scientific perspective,

separating specific neurophysiological components of
consciousness is necessary to clarify the psychological functions of the neural
mechanisms that regulate the brain’s large
-
scale networks.


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And from a philosophical perspective, we may find an opportunit
y to differentiate
consciousness into functional components, rather than assuming it is an indivisible
quality of mind.

But perhaps the most important opportunity is the interdisciplinary one: We are
working toward a scientific phenomenology in which an ob
jective, biological analysis
leads us toward a clearer appreciation of the bindings of consciousness in personal
experience.


Bibliography



Edelman, G. 1989.

The Remembered Present: A Biological Theory of Consciousness.

New York: Basic Books.




Holmes, M.
D., M. Brown and D. M. Tucker. 2004. Are “generalized” seizures truly generalized? Evidence of
localized mesial frontal and frontopolar discharges in absence.

Epilepsia

45(12):1568

1579.



Tononi, G., and C. Koch. 2008. The neural correlates of consciousness
: an update.

Annals of the New York
Academy of Science

1124:239

261.



Tucker, D. M., M. Brown, P. Luu and M. D. Holmes. 2007. Discharges in ventromedial frontal cortex during
absence spells.

Epilepsy and Behavior
11:546

557.



Tucker, D. M. 2007.

Mind From Bod
y: Experience From Neural Structure.

New York: Oxford University Press.





?

You can find this online at http://www.americanscientist.org/issues/num2/2011/1/fractures
-
and
-
bindings
-
of
-
consciousness/1

© Sigma Xi, The Scientific Research Society



KEY IDEAS to spot in this pap
er:




Every second, our brains take feedback from the world and provide
us with a sense of consciousness: awareness of what we are doing
and what we have just done.


o

Add to this “what we are about to do”





How this process works in the brain is no simple matter. But
sometimes examining how a process fails

as consciousness does in
people afflicted with epilepsy

enlightens us to how it works.


o

Key idea

in bio
logical approach is that “faults” in congenital (“b
orn
with”) and acquired (“occur during development”) “mechanisms”
reveal the underlying “substrate” of “normal”
(“functional, useful,
adaptive”) behavior


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The disruption of ongoing memory during an epileptic “
limbic seizure”
indicates tht this is a critical component of
consciousness, maintaining a
sense of continuity in time.



The disruption of volitional control of consciousness during

absence spells”
indicates that “intentionality” is a critical aspect of c
onsciousness is the
voluntary control of intentions. This component is closely related to, but
separable from, selective attention.



“localization” of brain functions or “mass action”
.

Are “psychological
functions, such as spatial memory and verbal reasoni
ng …localized in specific
brain regions, or do they emerge from the mass action of the brain as a
whole.”




“The human brain’s psychological operations are organized in relation to its
general architecture, which comprises a nested hierarchy of the evolved
structures… More recently evolved structures are stacked on top of more
primitive ones…”



SEIZURES:

(1)
generalized

tonic
-
clonic
seizures (
most severe … spre
a
d
)
a
nd
(2)
more localized
complex partial seizures
.

(temporal lobe epilepsy,
limbic seizures).



BINDING MEMORY
:
reasonable hypothesis: “the functional role of limbic
networks … is to regulate the memory process to ensure that motivationally
significant experiences are provided with adequate consolidation to be
retained in memory.”
……..

seizures disr
upt memory

o

“Without the continuity of recent memory, and the associated ability to anticipate the
immediate future, the temporal span of consciousness becomes vanishingly thin.”