Download Neural Correlate www.AssignmentPoint.com A neural correlate of a

Neural Correlate
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A neural correlate of a content of experience is any bodily component, such as
an electro-neuro-biological state or the state assumed by some biophysical
subsystem of the brain, whose presence necessarily and regularly correlates with
such a specific content of experience.
When the full ontological consistence or build-up of the reality variably called
mind, soul, psyche, or existentiality is called "consciousness" and deemed to
exclusively consist in mental contents associated with and at least partly
generated by the brain organ, the notion of neural correlate of consciousness is
commonly employed. When it is only the sensations that are held to be
produced by brain states, whether exclusively or not (e.g., when sensations are
also deemed capable of being generated by the mind reacting against itself),
then the notion of neural correlate of a content of experience is commonly
utilized. A mid-way concept, not always clarified, is that of a neural correlate
encompassing the production of every mental content but not of consciousness
itself.
Conceptual frameworks using the notion
The notion of a neural correlate of a mental state is an important concept for
materialists, those philosophers and researchers who believe that all mental
states are equivalent to brain states. According to strict materialists, all
properties credited to the mind, including consciousness, emotion, beliefs, and
desires have direct neural correlates. This is also a pragmatic view adopted by a
number of scholars. This view frequently depends on considering minds
exclusively as sentient knots in nature's causal net.
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Instead, other neuroscientists find minds inaugurating causal actions in nature,
rather than solely being able of merely continuing previously initiated causal
sequences. These neuroscientists thus describe minds as percipient agencies, the
mind's very agency or causal aptitude being deemed extraneous to any neural
correlate.
Still, some neurobiologists consider reasons to further assume that
rememberings are not engraved in brain tissue but retained by the very mind,
which thereby transforms itself in a way different from the time changes
underwent by non-minds. These later neuroscientists consider that there is no
neural correlate for episodal and some other memories, but that the mind moves
the brain state (like as it may also inaugurate a finger movement) in such a way
as to produce a brain state which the mind then reacts to by fleshing its selected
memory again (Husserl's Einfüllung), re-imagining it. This view develops a
notion by Aristotle and, again, makes no use of the notion of neural correlate for
certain experiences, namely in regard to complex mental contents. It only
admits neural correlates for the mind's elementary sensational reactions, which
are called "intonations" (following neurobiologist Christfried Jakob, 18661956).
The concept of a neural correlate only encompassing the production of
intonations occurs in a variety of researchers on different neurobiological
traditions, including Scholasticism (see References). Rather, the concept of a
neural correlate encompassing the production of every mental content occurs
only in a specific conceptual line of theoretical neuroscience, characterized by
the following features:
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 Minds are sometimes viewed as incapable of positing causal acts upon
self-initiated, internal modifications. This posits observers in nature as
epiphenomenal, unable to introduce perturbations, even less to absolutely
inaugurate causal series.
 Mental contents are considered stand-alone realities, similar to any other
physical reality as apples, rocks, or molecules. Such a line of opinion
does not admit a difference in level between non-mental things and
mental contents, namely that while things as apples and rocks do not
belong with any other natural reality and thus are capable of standing
alone, mental contents rather belong with a particular mind or, as
sometimes called, a particular existentiality: e.g., this red is in Jane's
experience whereas that red (which might be sensationally identical to
Jane's) is John's experience and not Jane's at all. This distinctive feature
of the contents of experience is dismissed (see Szirko's article cited in
References), so that the physical condition of mental contents is deemed
identical to the stand-alone condition of apples and rocks.
 The relationship of a mind with the body in which it finds itself is
platonistically portrayed, so that any a mind might have found itself in
any a brain-body system, like as a steerman may find himself in any ship
that he chances to steer. Therefore this line of theoretical neuroscience
does not admit that every mind and its particular body could intrinsically
make a unity besides and apart from their causal interactions, which
interactions, inasmuch as the mind is also deemed epiphenomenal, reduce
to bodily influences upon the mind's experiences or states.
 As a consequence, the connections of a mind and the body in which it
finds itself are deemed to exclusively be of causal-efficient nature, similar
to the energy supplied for a domestic appliance to function. This view
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entails that minds are no more than the mental contents which may be
causally generated in them by their respective brains. Sentience (minds'
intonability), semovience (minds' capability of inaugurating efficient
causal actions on internal forces) and circumstantiation (every mind's
finding itself in not another body) are thus viewed as highly problematic
and their research is usually relegated.
 In the conceptual line characterized by these four features, and in recent
years, papers have been published on the neural correlates of awareness,
emotions, and decision making. Francis Crick wrote a popular book "The
Astonishing Hypothesis" whose thesis is that the neural correlate for
consciousness lies in our nerve cells and their associated molecules. Crick
and his collaborator Christof Koch have sought to avoid philosophical
debates that are associated with the study of consciousness, by
emphasizing the search for "correlation" and not "causation".
There is much room for disagreement about the nature of this correlation (e.g.,
does it require synchronous spikes of neurons in different regions of the brain?
Is the co-activation of frontal or parietal areas necessary?). The philosopher
David Chalmers maintains that a neural correlate of consciousness, unlike other
correlates such as for memory, will fail to offer a satisfactory explanation of the
phenomenon.
Laboratory studies
Neurophysiological studies in animals provided some insights on the neural
correlates of conscious behavior. Vernon Mountcastle, in the early 1960s, set up
to study this set of problems, which he termed "the Mind/Brain problem", by
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studying the neural basis of perception in the somatic sensory system. His labs
at Johns Hopkins were among the first, along with Edward V.Evarts at NIH, to
record neural activity from behaving monkeys. Struck with the elegance of SS
Stevens approach of magnitude estimation, Mountcastle's group discovered
three different modalities of somatic sensation shared one cognitive attribute: in
all cases the firing rate of peripheral neurons was linearly related to the strength
of the percept elicited. More recently, Ken H. Britten, William T. Newsome,
and C. Daniel Salzman have shown that in area MT of monkeys, neurons
respond with variability that suggests they are the basis of decision making
about direction of motion. They first showed that neuronal rates are predictive
of decisions using signal detection theory, and then that stimulation of these
neurons could predictably bias the decision. Such studies were followed by
Ranulfo Romo in the somatic sensory system, to confirm, using a different
percept and brain area, that a small number of neurons in one brain area underlie
perceptual decisions.
Other lab groups have followed Mountcastle's seminal work relating cognitive
variables to neuronal activity with more complex cognitive tasks. Although
monkeys cannot talk about their perceptions, behavioral tasks have been created
in which animals made nonverbal reports, for example by producing hand
movements. Many of these studies employ perceptual illusions as a way to
dissociate sensations (i.e., the sensory information that the brain receives) from
perceptions (i.e., how the consciousness interprets them). Neuronal patterns that
represent perceptions rather than merely sensory input are interpreted as
reflecting the neuronal correlate of consciousness.
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Using such design, Nikos Logothetis and colleagues discovered perceptionreflecting neurons in the temporal lobe. They created an experimental situation
in which conflicting images were presented to different eyes (i.e., binocular
rivalry). Under such conditions, human subjects report bistable percepts: they
perceive alternatively one or the other image. Logothetis and colleagues trained
the monkeys to report with their arm movements which image they perceived.
Interestingly, temporal lobe neurons in Logothetis experiments often reflected
what the monkeys' perceived. Neurons with such properties were less frequently
observed in the primary visual cortex that corresponds to relatively early stages
of visual processing. Another set of experiments using binocular rivalry in
humans showed that certain layers of the cortex can be excluded as candidates
of the neural correlate of consciousness. Logothetis and colleagues switched the
images between eyes during the percept of one of the images. Surprisingly the
percept stayed stable. This means that the conscious percept stayed stable and at
the same time the primary input to layer 4, which is the input layer, in the visual
cortex changed. Therefore layer 4 can not be a part of the neural correlate of
consciousness. Mikhail Lebedev and their colleagues observed a similar
phenomenon in monkey prefrontal cortex. In their experiments monkeys
reported the perceived direction of visual stimulus movement (which could be
an illusion) by making eye movements. Some prefrontal cortex neurons
represented actual and some — perceived displacements of the stimulus.
Observation of perception related neurons in prefrontal cortex is consistent with
the theory of Christof Koch and Francis Crick who postulated that neural
correlate of consciousness resides in prefrontal cortex. Proponents of distributed
neuronal processing may likely dispute the view that consciousness has a
precise localization in the brain.
Neural correlates of cognitive variables
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In addition to neural correlate of consciousness in general, much progress has
been made in elucidating neural correlates of specific cognitive variables. Thus,
Earl Miller and colleagues discovered prefrontal cortex neurons that represent
perceptual categories (cats versus dogs in their experiments). The work of
Richard Andersen, Steven Wise, Carl Olson, Jun Tanji, Apostolos
Georgopoulos and other neuroscientists has illuminated neuronal correlates of
motor planning, selective visual attention, motor sequences and spatial reference
frames in which these entities are represented by brain cells. The progress in
understanding neuronal correlates of motor planning has led to the creation of
brain-machine interface so, the devices that translate neuronal activity into
purposeful commands to artificial actuators.
A large number of studies have addressed the problem of neural correlates of
mental
representations
in
human
subjects.
For
example,
functional
neuroimaging have shown that parts of the cortex are still active in vegetative
patients that are presumed to be unconscious (Laureys, Trends Cogn Sci, 2005,
9:556-559). However, these areas appear to be functionally disconnected from
associative cortical areas whose activity is needed for awareness.
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