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The degree of bimanual coordination that a person exhibits correlates positively with the connectivity between the two regions (Figure 8. Did the person become more coordinated because of the stronger connectivity, or has this difference in connectivity emerged because she engages in more bimanual activities, perhaps because she finds them more rewarding? Participants performed a bimanual coordination task, producing alternating taps with the two fingers. The tapping rate was varied such that, at high frequencies, the participants had trouble maintaining the pattern. Consider juggling, a skill that requires the coordination of the two hands, not to mention the ability to integrate complex spatial patterns created by the motions of the hands and balls. To the novice, juggling may seem impossible; but with just a modest amount of daily practice, most people can become quite skilled after a few months. When the jugglers stopped practicing, the gray matter volume in these regions of interest shrank, although it remained above the baseline level. Findings like these indicate that practice can readily shape the macroscopic landscape of the brain. Our parents and teachers may often remind us that practice makes perfect, but it is also hard not to argue that other factors are at play in determining expertise. Genetic polymorphisms have been associated with physiological differences that affect oxygen uptake and consumption, cardiac output, and muscle type and strength. One factor we tend to ignore when thinking about skilled performance is the importance of motivation. We consider how genetics might influence muscle size (and height if we are thinking about a sport like basketball), but there are also large individual differences in motivation: Some people are more willing to put in hours of practice than others. Although Galton defined motivation as "zeal," a more modern notion is that motivation is about the importance we place on action outcomes and their utilities (Niv, 2007). How much do we value the goal and its predicted reward relative to the cost we have to expend? Worth is subjective and has many variables, and in Chapter 12 we will consider this issue in detail. An interesting study of musical performers revealed that the most elite performers actually found practice less pleasurable than nonelite, but skilled, performers (Ericsson et al. One inference drawn from this work is that expertise requires not just hours of practice, but effortful practice in which the performer is constantly pushing him or herself to explore new methods or endlessly repeating the selected routine. Researchers find it easier to identify structural differences in experts in a physical activity-compared to , say, experts in theoretical physics- perhaps because we have a good idea of where we might expect to observe such differences. We can look in the hand area of the right motor cortex to see structural differences between violin players and musicians who play instruments that do not place such emphasis on lefthand fingering skills. Even so, we should be cautious in assuming such differences are at the heart of expertise. Across domains as diverse as motor skills, mathematics, and the arts, many commonalities are found among the most elite performers. A good explanation of the neural correlates of these commonalities has yet to be articulated. Learning and Performing New Skills 375 consequences of movement, it helps compensate for delays introduced by sensorimotor processing. Errors are derived from a comparison of the predicted and observed sensory information. The errors are used to update a forward model, a representation that can be used to generate the sensory expectancies for a movement. By anticipating the sensory the primary motor cortex is critical for the long-term retention of skills. Consolidation is enhanced by dopaminergic input to the motor cortex from the ventral tegmental area of the brainstem. Expertise is skill specific, but it may be more closely related to domain-independent factors such as motivation rather than a propensity, or inclination, for particular types of performance. Somatosensory input Summary Cognitive neuroscience has had a major impact on our conceptualization of how the brain produces skilled action. Nonetheless, this distributed pattern does not necessarily suggest that all of the systems operate in a similar way. As with other processing domains, like attention and memory, the different motor structures have their unique specializations.

However, language and visual perception emerge from sensory-perceptual systems; thus, it is easier to follow their progression when they are discussed with these systems. The sensory and motor systems represent the building blocks on which other systems are constructed and the raw material from which other systems draw; they are the most straightforward and best mapped systems. The systems we discuss in this chapter are integrated with the sensory-perceptual and motor systems but do not depend on any one modality. We refer to the systems here as higher order systems because, evolutionarily, the expression in humans is complex and highly integrated. Their functions are important for learning, organizing, setting priorities, planning, self-reflection, and self-regulation. The systems discussed in this chapter include the classic systems or modules of cognitive neuropsychology, namely memory, attention, and executive functioning. How you see yourself, to a large degree, is a product of the experiences of your life, the lessons you have learned, and what you remember as being important. Even what you tell yourself to remember to do in the future must incorporate memory. Stories of your personal and cultural past are stored in memory; thus, it is a necessary foundation of social communication. This section examines the various components of memory and what can happen when aspects of the memory system malfunction. But consider the question from a neuropsy- chological perspective: What do you lose if you lose your memory? Every time someone mentioned that his wife was dead, he relived the grieving experience. It is scary to imagine waking up and not knowing who you are, who your friends are, and what has happened in your life. Consider also what it might be like if you could not encode new information, if you could not remember what someone said 10 minutes ago, or if you could not register the information you needed to take a test or learn a new skill. Memory is an umbrella concept, and it is impossible to say categorically that someone has an overall good or bad memory. Neuropsychologists ask how the brain stores information over the long term and how it encodes, organizes, and then retrieves information from memory. Scientific understanding of normal memory processing in the brain has profited greatly from the study of people afflicted with various memory disorders, especially types of amnesia. The "soap opera" version of amnesia occurs when one of the characters gets hit on the head and promptly forgets who she or he is and all the specific episodes of her or his life. This character invariably wanders off to make a new life, including the development of a new identity. This type of memory deficit is reminiscent of a psychiatric dissociative state caused by severe emotional trauma, but it is not what occurs with neurologic injury or disease. Anterograde amnesia is the loss of the ability to encode and learn new information after a defined event (such as head injury, lesion, or disease onset). After the accident, she had difficulty learning new information (anterograde amnesia). Her mild retrograde amnesia is evidenced by her memory for driving out of the grocery store parking lot, which was about five blocks from the accident. Amnesias of this type are common in closed head injury (this condition is described further in Chapter 13). In general, anterograde (or a combination of anterograde-retrograde) amnesia is evident with brain injury. However, there are instances of retrograde amnesia with relatively spared anterograde learning and memory (Levine et al. Amnesia can be caused by a number of different problems and can take several forms. Sensory memory is fleeting, lasting only milliseconds, but its capacity is essentially unlimited in what may be taken in. Neuropsychological conceptualizations of memory generally do not consider sensory memory; rather, it is thought of as a component of sensory processing. Neuropsychology concerns itself with understanding how memory systems work in correspondence with known brain functioning.

As the cells reach their destination, they begin to develop the characteristics of the cell types that are intrinsic to that particular brain region (Kolb & Fantie, 1997). The process of increasing regional specialization of cells is referred to as differentiation. The open ends of the neural tube close at approximately the 26th day of gestation, with the anterior end subsequently creating the brain, and the posterior end forming the spinal cord. Failure of the neural tube to close during development can cause a number of developmental disorders. For example, neuroscientists believe that spina bifida, a congenital developmental disorder characterized by an opening in the spinal cord, results from a disruption of the proliferation rate of neural cells or from the failure of these cells to differentiate properly in the neural tube. The development of the cortex, corticogenesis, begins in the sixth to seventh embryonic week. The rapidly proliferating cells along the wall of the neural tube migrate outward at different predetermined times. The neurons migrate in sheets (laminae) along nonneuronal (glial) fibers that span the cortical wall. Ultimately, these neuronal sheets constitute the six laminated layers of the cortex and the subcortical nuclei. The inner layer forms first, followed by the development of the outer layers of the cortex. Each successive generation of migrating cells passes through the previously developed neuronal cells. Thus, the cortex develops from inside out, with migration beginning earlier for the more anterior and lateral areas of the cortex (Rakic & Lombroso, 1998). By the 18th week of gestation, virtually all cortical neurons have reached their designated locations and cell proliferation ceases. The exceptions are the cells of the hippocampus and cerebellum that continue to proliferate after birth (Anderson, Anderson, Northam, Jacobs, & Catroppa, 2001). After migration, many of the glia cells transform into astrocytes, whereas others merely disappear (Monk et al. Disruption in the migratory process can result in significant and extensive malformations of the developing brain. For instance, abnormalities of cell migration can produce developmental anomalies of the corpus callosum and other subcortical structures. Similarly, disruption of cell migration during the first trimester of development is associated with malformations of the cerebral cortex. An example is the condition of agyria, or lissencephaly, a disorder that occurs during the 11th to 13th weeks of gestation and involves the underdevelopment of the cortical gyri (Hynd, Morgan, & Vaughn, 1997). Severe neurologic problems accompany this condition, such as severe mental retardation, motor retardation, seizures, and reduced muscle tone. The intercommunications afforded by axonal connections are crucial to the integrative functioning of the brain. As the migrating neuronal cells reach their designated positions, dendrites begin to sprout in a process called arborization. Subsequently, little extensions called dendritic spines begin to extend out from the dendrites. The dendrites and dendritic spines create synapses for gathering information to transmit to the neuron. Dendritic growth begins prenatally and proceeds slowly, with the majority of arborization and spine growth actually occurring postnatally. The most intensive period of dendritic growth occurs from birth to approximately 18 months of age. The development of the dendrites and dendritic spines is highly sensitive to the effects of environmental stimulation. This sensitivity fosters the growth and differentiation of the brain; yet, it increases its vulnerability to damage.

If a person is asked to pantomime opening a drawer with one hand and to retrieve an object with the other, both hands may mime the opening Goal Selection and Action Planning 349 gesture. Again, this deficit fits with the idea of a competitive process in which an abstract goal-to retrieve an object from the drawer-is activated and a competition ensues to determine how the required movements are assigned to each hand. For example, the person may reach out and grab an object and then be surprised to find the object in her hand. In more bizarre cases, the two hands may work in opposition to one another, a condition that is especially prevalent after lesions or resection of the corpus callosum. One patient described how her left hand would attempt to unbutton her blouse as soon as she finished getting dressed. As we might expect, given its role in spatial representation, planning-related activity is also evident in the parietal lobe. Together, these results help reveal how action selection and movement planning evolve within parietofrontal pathways. In general, we see many similarities between posterior parietal cortex and premotor regions. For example, cells in both regions exhibit directional tuning, and population vectors derived from either area provide an excellent match to behavior. To take our coffee cup example, we need to recognize that reaching requires a transformation from vision-centered coordinates to hand-centered coordinates. To reach that object with the hand, however, we need to define the position of the object with respect to the hand, not the eyes. You can prove this to yourself by trying to reach for something with the starting position of your hand either visible or occluded. Physiological studies suggest that representations within parietal cortex tend to be in an eyecentered reference frame, whereas those in premotor cortex are more hand-centered (Batista et al. Another intriguing difference between parietal and premotor motor areas comes from a fascinating study that attempted to identify where intentions are formed and how we become aware of them (Desmurget et al. When the stimulation was over posterior parietal cortex, the patients reported that they experienced the intention or desire to move, making comments such as "I felt a desire to lick my lips. The patients did not produce any overt movement, and even careful observation of the muscles showed no activity. In contrast, stimulation of the dorsal premotor cortex triggered complex multi-joint movements such as arm rotation or wrist flexion, but here the patients had no conscious awareness of the action and no sense of movement intention. These researchers suggested that the posterior parietal cortex is more strongly linked to motor intention, the movement goals, and premotor cortex to movement execution. The signal we are aware of when making a movement does not emerge from the movement itself but rather from the prior conscious intention and predictions we make about the movement in advance of action. Each task activates both hemispheres, and we cannot keep the crosstalk created by these activation patterns from interfering with the movements. If this hypothesis is correct, spatial interference should be eliminated when each movement goal is restricted to a single hemisphere and the pathways connecting the two hemispheres are severed. To test this idea, Elizabeth Franz and her colleagues (1996) at the University of California, Berkeley, tested a patient whose corpus callosum had been resected. The stimuli for this bimanual movement study were a pair of three-sided figures whose sides followed either a common axis or perpendicular axes. Intact corpus callosum Callosotomy patient Common axis the stimuli were projected briefly-one stimulus appeared in the left visual field, the other in the right visual field. After viewing the stimuli, the participants were instructed to produce the two patterns simultaneously, using the left hand for the pattern projected in the left visual field and the right hand for the pattern in the right visual field. The brief presentation was used to ensure that each stimulus was isolated to a single hemisphere in the split-brain patient. In control participants, rapid transfer of information via the corpus callosum was expected. As Figure 1, top shows, control parPerpendicular axes ticipants had little difficulty producing bilateral movements when the segments of the squares followed a common axis of movement (upper left).