Connecting the self and the brain
Jan 8
Joseph LeDoux


Who are you? The answer, of course, lies in your brain. But how your
brain becomes and continues to be who you are is still poorly
understood. Neuroscientists have been quite successful in figuring
out how pieces of the brain puzzle work (perception, movement,
learning, emotion) but have not made much progress in putting the
pieces together to build the kind of global picture of brain function
that would be necessary to understand how one's personal identity,
one's self, is represented in neural tissue.

The self has been of more interest to philosophers and psychologists
than brain researchers. From Descartes through Locke and into modern

times philosophers have stressed consciousness as the defining aspect
of self. Carl Rogers, a pioneering self-psychologist, followed the
philosophers in defining the self as "the organised, consistent
conceptual gestalt composed of perceptions of the characteristics of
the 'I' or 'me"'. Many contemporary self-psychologists similarly
focus on self-consciousness. They do not deny that some aspects of
mental life occur unconsciously, but they tend to minimise the
importance of the unconscious.

Recently, there has been a growing interest in a more partitioned
view of the self. One partition is between the minimum and the
narrative self. The former is an immediate consciousness of one's
self; the latter a coherent self-consciousness that extends into the
past and future. But these conscious partitions, which themselves may
be based on different mechanisms, are, as Freud noted, only the tip
of the iceberg. Terms such as the primitive, core, ecological and non-
conceptual self, refer to unconscious aspects of personal identity
that define who we are. The study of implicit or unconscious aspects
of the self are now major themes in social psychology. In contrast to
the narrative and minimal self notions, which depend on language to
encode our awareness of who we are in consciousness, these implicit
aspects of the self are not accessible for verbal self-reflection.

Although the self has not been a major research interest for
neuroscientists, some have ventured into the territory. Michael
Gazzaniga and Antonio Damasio, for example, emphasise - as I do - the
importance of understanding the conscious self in the context of the
unconscious workings of the brain. But unlike Damasio and Gazzaniga,
whose ideas are about the organisation of the mind and experience, I
have been attempting to develop a theory that links the self to the
detailed understanding of the cellular basis of brain function that
is emerging

in neuroscience. Before I can explain this, though, I need to discuss
the relation of the self to consciousness in more detail.

Evolution of the self Consciousness, at least the kind of
consciousness we have in mind when we talk about our own mental
states, was very likely added to the brain in recent evolutionary
history. It was layered on top of all the other processes that were
already there in our animal ancestors. Although animals are not
conscious in the human sense, neither are they simply objects like
rocks or chairs. Non-human animals are living creatures with nervous
systems that represent external events internally and that allow
their bodies to interact with and change the material world. The
concept of a conscious person, a conscious self, while useful as a
way of evaluating issues related to being human (in assigning moral
and legal responsibility, for example), is less valuable as a concept
for understanding existence in the context of our animal ancestry.
When the self was viewed solely in terms of linguistically
constructed conscious experience, it was possible to ignore the
evolutionary links of the self to processes in other animals. But the
new view, emphasising non-verbal, non-conceptual, unconscious,
aspects of the self, requires an evolutionary context. To the extent
that many of the systems that function non-consciously in the human
brain function similarly in the brains of other animals, there is
likely to be considerable overlap in the non-conscious aspects of the
self between species. Obviously, the more similar the brains, the
greater the overlap. Having a self does not depend on having the
capacity to be self-aware.

While only humans have the unique aspects of the self made possible
by the human brain, other animals have the kinds of selves made
possible by their brains. We often talk about the personalities of
animals. One neighbour has a mean dog, another a lovely cat. We have
no trouble assessing the individuality of these creatures. And the
factors that go into the shaping of their personalities are similar,
up to a point, to those that shape ours. Because each biological
organism is unique, it will differ from other similar creatures. By
defining the self this way, we frame the problem in terms of
biological, and specifically brain, mechanisms.

Genes, synapses and experience The particular aspects of the self
that define "you" are present in your brain alone. In order for you
to remain who you are from minute to minute and year to year, your
brain must somehow retain the essence of who you are over time.
Memory is thus central to understanding the self in terms of neural
mechanisms. While memory implies the ability to recollect the past
consciously, the new view is that memory is stored by systems that
function both consciously (explicitly) and unconsciously
(implicitly). The self is, in essence, a complex set of implicit and
explicit memories.

In the late 19th century, a debate raged over whether the brain
contained individual cells that were interconnected or whether it was
composed of a mesh of continuously connected elements. Proponents of
the former theory, which emerged as the winner, included two great
pioneers in the study of the brain - Santiago Ramon y Cajal and
Charles Sherrington - as well as the young Sigmund Freud. The outcome
of this debate was not only the realisation that the brain is
composed of neurons, but also that connections between neurons, so-
called synapses, underlie all aspects of brain function.

Biologically, memories can be understood as changes in patterns of
connectivity between brain cells or neurons. Points of connection
between neurons are called synapses, tiny spaces through which the
brain does its business. Your memory of a particular experience
involves changes in the synaptic connections among the neurons that
are engaged by the stimuli that constitute the experience. To the
extent that the self is a set of memories, the particular patterns of
synaptic connections in an individual's brain and the information
encoded by these connections are the keys to who that person is.

Genes, too, make important contributions to personality and the self
by shaping the brain. All of the capacities that we have as homo
sapiens, including our capacities to learn and remember, are made
possible by the genetic make-up of our species. What we put in memory
systems as individuals is up to experience, but the existence and
basic mode of operation of these systems is due to our species'
genes.

At the same time, we each have a family genetic history that is a
variation on the theme of being a human, and a personal set of genes
that is a variation on our family's. All these variations influence
who we are.

The best-articulated view of the role of genes in shaping behavioural
and mental characteristics comes from biological trait theories of
personality. These propose that a person's enduring qualities are
caused by their genetic background. Considerable evidence has been
amassed to support the view that some traits, such as the extent to
which one is extroverted or introverted, are highly influenced by
one's genetic history. Nevertheless, genes usually account for at
most 50 per cent of any particular personality trait. For many traits
the influence is far less. Further, life's experiences, in the form
of learning and memory, shape how one's genotype is expressed. The
concept of phenotypic plasticity describes the fact that genes can
give rise to different outcomes in different circumstances. Even the
most ardent proponents of genetic determination of behaviour admit
that genes and environment interact to shape trait expression.

While the fact that both nature and nurture contribute to who we are
is widely acknowledged, less well understood is that, from the point
of view of how the brain works, nature and nurture are not different
things but different ways of doing the same thing: wiring synapses.
That is, both genes and experiences have their effects on our minds
and behavioural reactions by shaping the way synapses are formed.
Moreover, in many ways, the genetic influence on personality can also
be thought of as memory - a memory encoded across generations and
species rather than by individual experience. Synapses are the key to
both genetic and learned influences on who we are.

Progress in understanding the molecular biology of genes has led to a
surge of interest in the role of genes in brain function, including
the role of genes in personality. But it is important not to lose
sight of the contribution of experience, of learning and memory.
Through learning and memory processes, and the underlying synaptic
changes, personality builds up in a cohesive way. Without learning
and memory, personality would be an empty expression of our genetic
constitution. Learning allows us to transcend our genes.

Synaptic connections are also at the core of mental disorders. These
were long thought of simply as chemical imbalances. In fact, the key
is not the chemicals themselves, but the circuits in which the
chemicals act. For example, many drugs that are used to treat mental
disorders alter the monoamine class of chemicals in the brain
(serotonin, dopamine, norepinephrine, acetylcholine). These chemicals
are widely distributed across the brain, but the alterations that
affect a particular problem, such as schizophrenia, are now believed
to be restricted to a subset of the many circuits that use the
chemical in question. Systems and circuits are, in essence,
integrated sets of synapses.

Treatment of mental illness, whether by drugs or psychotherapy, is a
process of changing one's mental states and behaviours. Many of the
drugs used to treat depression and anxiety disorders affect the same
molecular cascades that have been implicated in learning and memory.
This suggests that drug therapy is a way of placing the brain in a
state conducive to learning.

Holding it all together If our self is encoded in the synaptic
connections of systems that function consciously and unconsciously,
will we know what a person is when we figure out how these systems
function? Actually, no. Figuring out the synaptic mechanisms
underlying each mental process is itself quite a challenge. But we
need to go beyond the mere explanation of how each process works in
isolation. We need to understand how the many processes interact, and
how the particular interactions that take place inside each of our
brains give rise to and sustain who we are. Synaptic interactions
between the systems that underlie the individual processes are key in
keeping the self integrated in space (across brain systems) and time
(across the days of our lives).

The integration problem is amplified by the fact that so many systems
in the brain are able to change as a result of experience. How is a
coherent personality ever established and maintained if different
systems are able to learn and store information on their own? Why
don't the systems come to function independently of one another? One
reason is that although the different systems have different
functions (seeing and hearing, controlling movements, planning and
decision-making, and so on) they experience the same world. They
process information differently, but about the same life events.

Another reason is the existence of convergence zones, regions that
are able to integrate the activity of other regions. Convergence
zones tend to engage in so-called higher-order processing. Not only
can convergence areas put information together, but they can also
send commands back to the lower-order systems, allowing some high-
level co-ordination across the specific systems.

Then there is the widespread nature of certain chemical systems, such
as monoamines. When these systems are turned on, they release their
chemicals throughout the brain. These chemicals can serve as signals
that facilitate learning across widely distributed systems. Monoamine
systems tend to be activated during significant events, such as
emotionally charged experiences. Indeed, activation of emotion
systems is one of the key ways that the self is glued together. The
brain has a number of emotion systems, including networks involved in
the identification of sexual partners and food sources, as well as
detecting and defending against danger. When one of these systems is
active, the others tend to be inhibited. For example, other things
being equal, animals will hang out in areas where they feel safe. So
when the time comes to search for food, their fear of certain
locations, like wide open spaces or places where they've previously
encountered a predator, might have to be overcome if that's where
food is likely to be found. The hungrier the animal, the more it will
tolerate fear and anxiety and take risks to get food. Similarly, both
hunger and sexual arousal are decreased by activation of systems
involved in fear and stress. But once aroused, sexual desire can
override many other brain systems - people risk all sorts of adverse
consequences for a fling. Not only does the arousal of an emotional
state bring many of the brain's cognitive resources to bear on that
state, it also shuts down other emotion systems. As a result, the
learning that occurs is relevant to the current emotional situation.

The broader the range of emotions that a child expresses, the broader
will be the emotional range of the self that develops. This is why
childhood abuse is so devastating.

If a significant proportion of early emotional experiences are caused
by activation of the fear system, then the characteristic personality
that begins to build up from the parallel learning processes co-
ordinated by the emotional state is one drenched in negativity and
hopelessness rather than in affection and optimism. Similarly,
dissociative states that exist in certain forms of mental disorder
might be thought of as emotionally driven synaptic configurations
that partition the mind and behaviour in abnormal, maladaptive ways.

Most of us, most of the time, are able to piece together synaptic
connections that hold our selves together. Sometimes, though,
thoughts, emotions and motivations come uncoupled. When this happens,
the self is likely to begin disintegrating, and mental health to
deteriorate. When thoughts are radically dissociated from emotions
and motivations, as in schizophrenia, personality can change
drastically. When emotions run wild, as in anxiety disorders or
depression, you are no longer the person you once were. And when
motivations are captured by drug addiction, the emotional and
intellectual aspects of life suffer.

Thinking broadly about who we are Given the importance of synaptic
transmission in brain function, it's practically a truism to say that
the self is synaptic. What else could it be? But not everyone will be
happy with this conclusion. Many people will counter that the self is
psychological, social or spiritual, rather than neural, in nature. My
assertion that synapses are the basis of personality does not assume
that your personality is determined by synapses; it's the other way
around. Synapses are simply the brain's way of receiving, storing and
retrieving our personalities, as determined by all the psychological,
cultural and genetic factors. So as we begin to understand ourselves
in neural, especially synaptic, terms, we do not have to sacrifice
the other ways of understanding existence. A neural understanding of
human nature broadens rather than constricts our sense of who we are.

PROSPECT

Joseph LeDoux is a professor at the Centre for Neural Science, New
York University, and the author of The Synaptic Self: How Our Brains
Become Who We Are (Macmillan, $66).

http://afr.com/review/2003/01/08/FFXAVQHOMAD.html