My Stroke of Insight: A Brain Scientist's Personal Journey (3 page)

The two hemispheres communicate with one another through the highway for information transfer, the corpus callosum. Although each hemisphere is unique in the specific

types of information it processes, when the two hemispheres are connected to one another, they work together to generate a single seamless perception of the world.

When it comes to the intricate microscopic anatomy of how our cerebral cortices are finely wired, variation is the rule, not the exception. This variation contributes to our individual preferences and personalities. However, the gross (or macroscopic) anatomy of our brains is quite consistent and your brain looks very similar to mine. The bumps (gyri) and grooves (sulci) of the cerebral cortex are specifically organized such that our brains are virtually identical in appearance, structure, and function. For example, each of our cerebral hemispheres contain a superior temporal gyrus, pre-and postcentral gyri, a superior parietal gyrus, along with a lateral occipital gyrus - just to mention a few. Each of these gyri are made up of very specific groups of cells that have very specific connections and functions.

For instance, the cells of the postcentral gyrus enable us to be consciously aware of sensory stimulation, while the cells in the precentral gyrus control our ability to voluntarily move our body parts. The major pathways for information transfer between the various cortical groups of cells (fiber tracts) within each of the two hemispheres are also consistent between us and, as a result, we are generally capable of thinking and feeling in comparable ways.

The blood vessels supplying nutrients to our cerebral hemispheres also display a defined pattern. The anterior, middle, and posterior cerebral arteries supply blood to each of the two hemispheres. Damage to any specific branch of one of these major arteries may result in somewhat predictable symptoms of severe impairment or complete elimination of our ability to perform specific cognitive functions. (Of course there are unique differences between damage to the right and left hemispheres.) The following illustration shows the territory of the middle cerebral artery of the left hemisphere, and this includes the location of my stroke. Damage to any of the middle cerebral artery's primary branches would result in relatively predictable symptoms no matter who was having the problem.

The superficial layers of the cortex, which we see when we look at the external surface of the brain, are filled

with neurons that we believe to be uniquely human. These most recently "added on" neurons create circuits that manufacture our ability to think linearly - as in complex language and the ability to think in abstract, symbolic systems like mathematics. The deeper layers of the cerebral cortex make up the cells of the limbic system. These are the cortical cells we share with other mammals.

The limbic system functions by placing an affect, or emotion, on information streaming in through our senses. Because we share these structures with other creatures, the
lim
bic system cells are often referred to as the "reptilian brain" or the "emotional brain." When we are newborns, these cells become wired together in response to sensory stimulation. It is interesting to note that although our
lim
bic system functions throughout our lifetime, it does not mature. As a result, when our emotional "buttons" are pushed, we retain the ability to react to incoming stimulation as though we were a two year old, even when we are adults.

As our higher cortical cells mature and become integrated in complex networks with other neurons, we gain the ability to take "new pictures" of the present moment. When we compare the new information of our thinking mind with the automatic reactivity of our limbic mind, we can reevaluate the current situation and purposely choose a more mature response.

It might be of interest to note that all of today's "brain-

based learning" techniques used in elementary through high school capitalize on what neuroscientists understand about the functions of the limbic system. With these learning techniques, we try to transform our classrooms into environments that feel safe and familiar. The objective is to create an environment where the brain's fear/rage response (amygdala) is not triggered. The primary job of the amygdala is to scan all incoming stimulation in this immediate moment and determine the level of safety. One of the jobs of the cingulate gyrus of the limbic system is to focus the brain's attention.

When incoming stimulation is perceived as familiar, the amygdala is calm and the adjacently positioned hippocampus is capable of learning and memorizing new information. However, as soon as the amygdala is triggered by unfamiliar or perhaps threatening stimulation, it raises the brain's level of anxiety and focuses the mind's attention on the immediate situation. Under these circumstances, our attention is shifted away from the hippocampus and focused toward self-preserving behavior about the present moment.

Sensory information streams in through our sensory systems and is immediately processed through our limbic system. By the time a message reaches our cerebral cortex for higher thinking, we have already placed a "feeling" upon how we view that stimulation - is this pain or is this pleasure? Although many of us may think of ourselves as
thinking creatures that feel,
biologically we are
feeling creatures that think
.

Because the term "feeling" is broadly used, I'd like to clarify where different experiences occur in our brain. First, when we experience
feelings
of sadness, joy, anger, frustration, or excitement, these are emotions that are generated by the cells of our limbic system. Second, to
feel
something in your hands refers to the tactile or kinesthetic experience of feeling through the action of palpation. This type of feeling occurs via the sensory system of touch and involves the postcentral gyrus of the cerebral cortex. Finally, when someone contrasts what he or she
feels
intuitively about something (often expressed as a "gut feeling") to what they think about it, this insightful awareness is a higher cognition that is grounded in the right hemisphere of the cerebral cortex. (In Chapter Three we will discuss more thoroughly the different ways in which the right and left cerebral hemispheres operate.)

As information processing machines, our ability to process data about the external world begins at the level of sensory perception. Although most of us are rarely aware of it, our sensory receptors are designed to detect information at the energy level. Because everything around us - the air we breathe, even the materials we use to build with, are composed of spinning and vibrating atomic particles, you and I are literally swimming in a turbulent sea of electromagnetic fields. We are part of it. We are enveloped within it, and through our sensory apparatus we experience
what is.

Each of our sensory systems is made up of a complex cascade of neurons that process the incoming neural code from the level of the receptor to specific areas within the brain. Each group of cells along the cascade alters or enhances the code, and passes it on to the next set of cells in the system, which further defines and refines the message. By the time the code reaches the outermost portion of our brain, the higher levels of the cerebral cortex, we become conscious of the stimulation. However, if any of the cells along the pathway fail in their ability to function normally, then the final perception is skewed away from normal reality.

Our visual field, the entire view of what we can see when we look out into the world, is divided into billions of tiny spots or pixels. Each pixel is filled with atoms and molecules that are in vibration. The retinal cells in the back of our eyes detect the movement of those atomic particles. Atoms vibrating at different frequencies emit different

wavelengths of energy, and this information is eventu coded as different colors by the visual cortex in the occi region of our brain. A visual image is built by our br ability to package groups of pixels together in the form edges. Different edges with different orientations - vert horizontal, and oblique, combine to form complex ima Different groups of cells in our brain add depth, color, motion to what we see. Dyslexia, whereby some wr letters are perceived in reverse from normal, is a g example of a functional abnormality that can occur when normal cascade of sensory input is altered.