CHAPTER 43 BRAIN LATERALITY

BRAIN LATERALITY AND ASYMMETRY

“The brain, including the amygdala and orbitofrontal cortex (responsible for the assignment of meaning to stimuli), the hippocampus (the major center for conscious, declarative, explicit memory processing), and the lateral prefrontal cortex (thought to be a primary center for focal, conscious attention), is divided into two halves.  At various points, bands of tissue, including the corpus callosum and the anterior commissures (and, indirectly, the cerebellum), connect the left and right halves of the brain.  The uppermost part of the brain is called the cerebrum and includes the area called the neocortex, where complex thinking is believed to reside.  Each half of the upper brain can be referred to as a “cerebral hemisphere.”  In this book, the terms “right” or “left” as applied to brain, cortex, hemisphere, side, or mode refer in general to the specialized anatomy or functions of that side of the entire brain:  from the abstract processes at the top of the brain, to the more basic physiological and sensory ones lower down, emanating from the brainstem.

“…asymmetries exist within the brainstem and limbic system long before neocortical development.  These intrinsic differences may have direct effects on the unfolding of asymmetric representational capacities, including the more abstract processes of the neocortex.  The predominance of the ventral or dorsal pathways within each hemisphere may shape the motivational bias of attention and memory within that stream of information.  Although certain functions appear to be specialized in each half, the normal functioning of the mind involves “cross-talk” between the two sides of the brain.  The connecting tissue between the hemispheres appears to be important for both mutual activation and inhibition of corresponding (“homologous”) cerebral centers on (siegel/tdm/178) either side of the brain….the way in which modes of processing interact with each other cooperatively, interact conflictually, or remain rigidly dis-associated may play a large role in qualitative experience of mental functioning and well-being.  (siegel/tdm/179)”

“…two “streams” of information…have evolved between the cortex and deeper structures [of the brain] via the frontal lobes….Though each of these trends is present on both sides of the brain, the dorsal pathway appears to be predominant on the right side of the brain, and the ventral pathway on the left side.  (tdm/175)”

“…studies suggest a role of inhibition of the asymmetric corticolimbic dorsal and ventral pathways, rather than merely an activation of one side or the other [in regard to the intensity and kind of emotion experienced on either side].  Furthermore, each hemisphere may be involved in contralateral inhibition – negative affect on the right side may actually be demonstrating release of the inherent emotion of the opposite side…”  (siegel/tdm/183)

“These views allow us to understand the notion of “cognitive representations” in a developmental light:  Neocortical capacities to represent reality between perception and action emerge in the setting of powerful and asymmetric intrinsic motivational factors built into the structure and function of the brain.  These motivational systems influence embryonic growth and postnatally depend on interpersonal experiences for their continued differentiation.  (siegel/tdm/176)”  …these genetically driven asymmetries create their own subjective and interpersonal effects on human experience.  (siegel/tdm/177)”

“Emotion exists on both sides of the brain.  Research on emotion…demonstrates the intimate influence of emotion on all cognitive processes, from attention and perception to memory and moral reasoning.  (siegel/tdm/181)”

“…appraisal and arousal circuits, the value centers of the brain, are located on both sides.  For these re- (siegel/tdm/182) sons, it is fair to say that both sides of the brain are filled with meaning and emotional processes.  The qualitative ways in which each hemisphere is influenced by these neuronal activations – the essence of primary emotions – may be quite distinct because of the representational processes that are unique to each side. (siegel/tdm/183)”

“…motivational factors are asymmetric from prenatal development onward, and that the value systems on each side of the brain push experience and development in specific directions.  (siegle/tdm/183)”

“Emotional processes are a fundamental part of both hemispheres and are not restricted to only one side or one area of the brain.  Our abilities to perceive primary emotional states, and to become both conscious of them and able to translate them into expressions to others, may be at the heart of the qualitative difference in the experience of emotion between the hemispheres.

The whole brain creates the mind.  In neurologically intact individuals, the activity of both sides of the brain contributes to the functioning of the brain as a whole with greater or lesser degrees of interdependent activity.  Just as…certain mental systems can function in association (such as explicit and implicit memory), in some conditions there is a dis-association in functioning.  The mental systems, modules, or modes carrying out the functions of the mind probably emanate from the activity of the intricate circuitry in specific regions of the brain.  Examining the location of these modules an only help us understand human experience.  The studies of laterality offer a powerful tool in understanding the mind.  (siegel/tdm/185)”

“Women have for facility in classically left-hemisphere processes, and men in right-hemisphere ones….females tend to have more processes that are bilaterally distributed.”  (siegel/tdm/191)

“Exposure to hormones during fetal growth is felt to be one factor that directly influences the specialization of hemispheric function.  Studies have found that lateralization probably occurs before birth….”  Tdm/191  (possible connection to my thoughts on my “vision” and first glimpse, that I know of, of a self in the future – experience possibly mediated by hormones)

“In professional musicians, the study of music appears to involve the growth and development of parts of the brain in a different manner from their development in the casual music listener.  Specifically, (siegel/tdm/193) the left brain’s language-based, analytic mode becomes a more dominant part of the music experience with education and formal training.  This appears to involve judgments about duration, sequence, and rhythm.  In contrast, the right side’s ability appears to be stronger in the areas of tonal memory, melody recognition, and intensity.  (siegelt/dm/194)”

“In their essential features, Levy argues, the spatial abilities of the right hemisphere are directly conflictual with the linguistic representations of the left.  According to this “cognitive crowding hypothesis,” keeping the right mode separate from the left allows for the existence of two extremely different but vital and important ways of knowing.  In this manner, the isolation of the two hemispheres is required in order to achieve the unique information-processing modes of each side of the brain. (siegel/tdm/197)”

“This asymmetry of the brain creates a functional contrast between familiarity on the left and novelty on the right……….how distinct these two ways of knowing are [talks about Drawing on Right Side of the Brain]  (siegel/tdm/198)”

“…the issue of “left brain or right brain” is not even really important in the final analysis.  What we are concerned with is the subjective experience of minds, not merely the functional anatomy of the brain.  It is indisputable that there are two profoundly different modes in which the mind processes information.  One or the other mode can dominate our conscious experience at various times.  The finding that these modes of the mind do indeed have robust correlations with the sides of the brain just helps us to understand the probable neurophysiological mechanisms underlying what has been know for hundreds of years.

“Neuroscience can also help us avoid excessive generalizations about bilaterality”.  Our different ways of knowing intermingle in our daily lives.  Creativity does not come from only one mode or the other.  Happiness or other emotions do not emerge from living only in the timeless, nonverbal mode of constructing reality.  Success does not emerge solely from the linguistic, controlled, and well-defined rules of the other mode….an emergent quality of living a vital and flexible life may come from an openness to bilateral functioning involving many ways of knowing.  (siegel.tdm/199)”

“Just as the mind can isolate implicit recollections from explicit ones, so too can it isolate right- from left-hemisphere functions.  Hemispheric dis-association can be understood as a domination of one mode over the other.  (siegel/tdm/204)”

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“How are these bilateral processes relevant to relationships?  Communication is crucial in establishing neural connections early in life and involves the sharing of energy and information.  Levels of arousal (energy) and mental representations (information) are very different on each side of the brain.  The sharing of arousal and representations from one brain to another – the essence of connecting minds – will thus differ between the hemispheres.  One can propose, in fact, that the right brain perceives the output of the right brain of another person, whereas the left brain perceives the left brain’s output.  In intimate, emotional relationships, such as friendship, romance, parent-child pairs, psychotherapy, and teacher-student dyads, what does this look like?  The left brain sends out language-based, logical, sequential interpreting statements that attempt to make sense of things.  The left brain receives these messages, decodes the linguistic representations, and tries to make sense out of these newly arrived digital symbols.  At the same time, the right brain is sending nonverbal messages via facial expressions, gestures, prosody, and tone of voice, which are perceived by the other’s right brain.  OK.  So what?  (siegel/tdm/205)”

“The “what” of it is that the right brain takes this information and uses its social perceptions of nonverbal communication to engage directly in a few very important processes.  It creates an image of the other’s mind (“mindsight”). It regulates bodily response while (siegel/tdm/205) at the same time registering the somatic markers of the shifts in bodily state.  It creates autobiographical representations within memory.  It appraises the meaning of these events and directly affects the degree of arousal, thus creating primary emotional responses.  Intense and primary emotional states are therefore likely to be mediated via the right hemisphere.  (siegel/tdm/206)”

“When we examine these findings alongside the independent set of data from attachment research, certain patterns are suggested.  The early affect attunement and alignment of mental states can be seen as a mutually regulated hemisphere-to-hemisphere coordination between child and parent.  In this view, we can propose that avoidant attachment involves a serious lack of this form of communication between the right hemispheres of child and parent.  The extension of this finding to laterality research raises the possibility that the left hemisphere serves as the dominant mediator of communication between avoidant child and a dismissing parent…  [end of sentence, not end of paragraph] . (siegel/tdm/206)”

“If this laterality-attachment hypothesis is correct, then a logical implication would be that any experiences that help to develop the processing abilities of each hemisphere and/or the integrated activities of the two hemispheres may improve certain individuals’ internal (siegel/tdm/206) and interpersonal lives.  Such movement toward more coordinated interhemispheric functioning would be quite welcomed by many people (especially by the lonely and frustrated spouses [and offspring] of dismissing individuals).  The developmental and experiential histories that led to a lack of integration of the functioning of the two hemispheres may leave individuals vulnerable to emotional and social problems.  Unresolved trauma and grief, histories of emotional neglect, and restrictive adaptations may each represent some form of constriction in the flow of information processing between the hemispheres. [why is he not mentioning disorganized?]  This proposal of the central role of dis-associated hemispheric processing in emotional disturbances is supported by the finding that insecure attachments in childhood may establish a vulnerability to psychological dysfunction.  (siegel/tdm/207)”

“Emotional relationships that enhance the development of each hemisphere and its unrestricted integration with the activity of the other can thus be proposed to be likely to foster the development of psychological well-being.  In this way, a secure attachment can be seen as a developmental relationship that provides for an integration of functioning of the two hemispheres, both between child and caregiver and within the child’s own brain.  At the most basic level, right-hemisphere-to-right-hemisphere communication can be seen within the affectively attuned communications that allow for primary emotional states to be shared via nonverbal signals.  Left-hemisphere-to-left-hemisphere alignment can be seen in shared attention to objects in the world.  [Does this have anything to do with how depersonalized I feel, and that I don’t feel connected to place, home, or much even to things?]  Reflective dialogues, in which language is used to focus attention on the mental states of others (including the two members of the dyad), may foster bilateral integration between the two hemispheres of both child and parent.  The resilience of secure attachments can thus be proposed as founded in part in the bilateral integration that these relationships foster.  (siegel/tdm/207)”