Research Of The Brain Development And Changes In Adolescents
Adolescence refers to a transition from childhood to adulthood where physical changes occur in the body and brain, although these physical changes during puberty does not equate to adolescence. Adolescence is a unique time in brain development, characterized by increases in white matter, myelination, and changes in sub-cortical functional connectivity strength, to name just a few of the important changes occurring. Adolescence is not culture-specific, and this coming of age period is recognized with different traditions and new responsibilities for adolescents in nearly all cultures. In fact, almost all mammals go through some sort of adolescent period. Researchers and the general population alike have recognized for decades that the adolescent brain is different from a fully-developed adult brain. Indeed, parents of adolescents have nearly all experienced teenagers engaging in risky and impulsive behaviors, while navigating a desire for increased autonomy and independence from their parents. At the same time as these changes in impulsivity and autonomy, teens are also often making important life decisions. The behavioral and emotional changes seen among adolescents are well-documented, however, researchers did not have the capacity to study changes in the brain until more recently. Improved technologies have allowed for fMRI studies to take place. The most promising version of MRI studies to assess the presenting question is structural MRI, or sMRI. Structural MRI would be the most appropriate to identify 18-year-old recruits, given its ability to look at the size/level of development of different things in the brain.
Structural MRI is able to detect how much gray matter (cell bodies) and white matter (myelin, fatty sheath on axons), and see how big structures are or how much gray/white matter there is in the brain. Since 18-year olds are not fully developed in terms of their brain structures yet, it is important to have tools like sMRI to be able to screen for more mature brains. The sMRI screenings that will occur at DARPA will look at the myelination levels in each brain, as myelinated cells are more efficient In carrying messages to the brain. sMRI would also need to look at changes in subcortical-cortical functional connectivity strength, ventral attention networks, and somatomotor networks (which each increase their modularity across adolescent development).
Neuroplasticity refers to the brain's ability to change structurally to accommodate experiences, whether the experience involves accommodating large amounts of navigating (such as in London taxi drivers with significantly more gray matter in the hippocampi --particularly the right hippocampus, associated with spatial navigating/memory), or whether it involves adapting after an amputation or major injury. The brain can change structurally in remarkable different ways, including the creation of new neurons (neurogenesis), or redistribution of the cells, or the cells growing in size.
In the present scenario, Rick Allen demonstrated great adult neuroplasticity following his left arm amputation. Just like how London cab drivers demonstrated plasticity with their posterior hippocampus relative to non- cab drivers, Rick Allen's brain structures were likely affected by his accident and history with his experiences as a musician. The corpus callosum, which is related to interhemispheric communication between the two brain hemispheres, was likely affected, specifically in his anterior region of the corpus callosum. In order for Allen to be able to re-learn to drum, and use a completely different arm, his two hemispheres would need to be very flexible (since he used his left hand to drum before). Playing music requires integrating sensory with motor information, and also paying attention to one's performance at the same time, which requires both of the hemispheres. In Allen's case, his situation also required him to have flexibility with his handedness, and even learn to use his feet (a limb he had never used to make music before). His plasticity is evident in the motor flexibility of the limbs that he had to learn to use and integrate.
Oliver Sacks' term "the remarkable endurance of self" refers to the integration of vision, vestibular sensation (balance organs), and proprioception to support one's own sense of self. In each of the following examples, a major component of Sacks' "remarkable endurance of self" has undergone damage, resulting In damage to one's own sense of self, and body ownership status/beliefs. Blindsight refers to a condition in which someone is blind or very nearly blind, yet can still make use of very simple visual information. In the example from class, his phylogenetically primitive “orienting” pathway was still intact, even though the “new” pathway (the pathway containing the primary visual cortex that leads to conscious experience) is not. Our character discussed in class "Drew" was able to point at things he said that he could not see, and was able to name the orientation of objects at rates better than by chance (even though when asked, "What Is this?" he did not know). The zombie in the brain refers to our use of the old visual pathway. Someone with blindsight has an altered sense of self, specifically with regards to conscious awareness of what you are seeing. Christina was a patient who was unsteady on her feet, was extremely clumsy and often dropped things, and had essentially no coordination abilities. Christina could not stand unless she looked directly at her feet, and she could not hold anything in her hands unless she kept a close eye on them. Christina's case study represented a person who did not undergo brain damage, but Instead was Impacted by neurological damage. In Christina's case, she had lost all proprioception. She had no muscle or tendon or joint sense, and also experienced a slight loss in other sensory modalities.
The loss of Christina's proprioception contributed greatly to the loss of Oliver Sacks' term "the remarkable endurance of self. " Proprioception refers to a sense of relative position of different neighboring parts of the body/organs. In people with intact proprioception, even a blindfolded person knows through proprioception where their limbs are. The vestibular system provides the body with a sense of balance and spatial orientation for coordination and movement, as well as balance. In Christina's case, she had lost her proprioception because her brain was no longer integrating proprioception information with the information from her vestibular system, and this eroded her overall sense of body movement and positioning. In Arthur's case, he suffered from Capgras' delusions, which caused him to regard his close acquaintances as imposters even though he was very bright. In many patients, these types of delusions occurs after a traumatic brain lesions (although it can sometimes be spontaneous). Additionally, most patients believe that their parents, children, spouses, or siblings are imposters. Arthur's pathways associated with visual recognition and emotions in the brain were damaged (disconnected from the amygdala), while his auditory cortex was intact. He would recognize his parents on the phone only, but due to damage in the connections between the "face region" of the brain and his amygdala, his temporal cortex could not recognize the image to pass on to the amygdala, so information never got to his limbic system. Arthur's ability to link emotions to faces had been eroded in this case study. He was distressed by seeing his mother but not having any emotion towards her, so his brain assumed the person only resembles his mother (an "imposter").
The case of H. M. contributed to our current understanding of memory in several distinct ways. Despite H. M. ’s debilitating memory impairments, particularly in spatial memory, declarative, and episodic memory), he was able to successfully acquire a motor skill. For example, although he did not have the declarative memory to say he had done the mirror task, it was obvious to him that he had done it before when he did it again. This helped researchers better understand that memory is not a single thing. Instead, there are different types of memory, such as declarative (when H. M. was not able to verbally state that he had done it), procedural memory (H. M. was able to do the task more easily after already doing it), and other types of memory such as semantic memory (the things that people have perfected as a result of learning, including concepts, vocabulary, numerical processes, facts).
H. M. 's classic case also helped researchers to learn that memory is separate from intellectual and perceptual functioning. The structures damaged in memory-impaired patients were thought not to be involved in intellectual and perceptual functions after studying the case of H. M. They observed that his IQ went up after his brain surgery, and hypothesized that his score improved because he was not having seizures anymore. H. M. 's personality did not change much throughout all of these events, and he was still easygoing with a mild temperament. H. M. also formed the basis for our current understanding that the medial temporal lobe structures are not relevant in immediate memory, or in other words for the rehearsal and maintenance of material in short time periods (this is now referred to as working memory). H. M. had considerable abilities in areas such as sustained attention, which included the ability to retain information for a period of time after it was first encountered. He also demonstrated a strength in puzzle work.
Overall, H. M. 's memory impairments were really under fairly good control, only impacting certain areas while the other areas described above remained strengths. Another major principle of memory that H. M. helped to elucidate is long-term memory, and specifically he helped address questions about where long term memory information is stored. We learned from H. M. that the medial temporal lobe cannot be the ultimate storage site for long-term memories. Long-term memories must be stored elsewhere. The researchers were able to draw this conclusion because H. M. appeared to have good access to facts and events from time periods isolated from his surgery.
The mirror neuron system in the human brain were originally described as visuomotor neurons that fire when an action Is performed, while simultaneously a similar or identical action is observed passively. The neuron "mirrors" the behavior of the other, as though the observer were acting itself. Mirror neurons have been implicated in neurological and psychiatric disorders such as MS, Autism, and alexithymia. The premotor cortex and the Inferior parietal complex have both been shown to have brain activity thought to be consistent with that of mirror neurons, and the areas involved in the mirror neuron system In the human brain include more specifically include a supplementary motor area, primary somatosensory cortex, inferior parietal cortex, and the ventral premotor area. There is also Evidence for consistent activation in the left and right inferior frontal gyrus, the ventral premotor cortex, superior parietal lobule, dorsal premotor cortex, and the inferior parietal lobe. Ramachandran believes that mirror neurons contribute to human imitation abilities, and the ability to adopt someone else's point of view. In order to imitate a complex act, one must adopt the other person's point of view. In terms of human social interactions and human culture, mirror neurons are thought to be at play when humans learned to use tools, build shelter, and also in theory of mind and empathizing with someone when they are touched. Without the ability to see oneself in another's shoes, and adopt a simulation of that person's actions in your mind, humans would not have been able to learn from one another when it was essential to. Individuals who are not able to mirror the behavior of others would not have had the ability to make shelter, find food, use tools, and more. Indeed, mirror neurons play an important role in meeting these basic human needs, and contribute to better likelihood of individual survival by doing so.
Sense of humor refers to the brain’s capacity to perceive, relate, and experience a situation and judge that situation, while laughter is a vocal expression that responds to humor (an involuntary mental event). Laughter is thought to be regulated by a higher-level linguistic process (unlike the lower level processes governing the vocal motor system), which is thought of as a laughter-specific center and is located in the dorsal upper pons. This system coordinates messages from two partially independent pathways; one is involuntary and involves the amygdala and thalamic (hypo and subthalamic) areas, and the other is voluntary (originating in the premotor/frontal areas and also involving the motor cortex and ventral brainstem). Researchers' evidence for this higher-level linguistic process lies in the fact that sense of humor is learned, and laughter is a response to this learned ability to judge whether situations are humorous. Sense of humor is acquired/learned as our mental abilities develop during middle to late childhood. So, sense of humor is a mental and intellectual skill, and laughter arising out of humor is conditional. Because laughter Is conditional, it is thought to depend on the person’s intellectual ability. Laughter is thought to have evolved as a way to establish and strengthen bonds, quickly and effectively, and also to deal with the stressors and social demands of living socially in a large group. This is the basis of the Social Brain Hypothesis. Ramachandran also believes that laughter contributes to a false alarm system, alerting others that something alarming has just happened, and that it can be ignored. It is also implicated as a self-defense mechanism, especially cognitively. This can be seen in the "nervous laughter" phenomenon. From an evolutionary standpoint, laughter contributes to survival because when people have a tool to create strong bonds rather quickly, it reduces the chances that group members will become angry with one another and/or fight. If humans did not have strong bonds while we were evolving, there would certainly be higher chances of being killed or hurt by a group member living with you. Laughter buffers against this.
Unique specializations in each of the two hemispheres in the brain are thought to date back to 500 million years ago, when vertebrates evolved. The right hemisphere is primarily concerned with emotional arousal (threats from predators, etc. ), and the right hemisphere is known to attend to environmental input. The left hemisphere specializes more in familiar things (language and self-motivated behaviors) and primarily is concerned with internal states (vs. environmental). The "big picture" refers to one's sense of everything on both sides of your body, and can also be described as attending to the "whole scene. " In order to attend to the "big picture", global aspects of the environment, vs. limited and detailed features, need to be acknowledged by the observer. Thus, the right hemisphere is the hemisphere thought to see the "big picture. " Memories stored by the right hemisphere tend to be organized and recalled as a general pattern, while in contrast, the left hemisphere is skilled in focusing on local aspects of the environment. Evidence lies in studies on brain hemispheres in humans, and also animals. In Delis' experiment, the patients with damage to the right hemisphere often scattered A’s over the page. In contrast, patients with damage to the left hemisphere only drew a large capital “H”. This experiment shows that the left hemisphere characterized stimuli according to a few details, whereas the right brain synthesized the observed global patterns. If the left hemisphere is compromised/damaged, the right hemisphere can compensate (due to its ability to take in global information). The same happens vice versa, but not usually with as strong of a compensation. This supports hemispheric specialization from an evolution standpoint. The president's speech example from class also supports the "big picture" ability of the right hemisphere. The right hemisphere deals with non-verbal aspects of language, so those with left hemisphere damage may pay attention to tones, but not content. This is an example of an aphasia, or the inability to comprehend and/or formulate language because of damage to a specific brain region. People with a non-damaged right hemisphere would likely interpret a speech, such as the president's speech example, more accurately than those with a damaged right hemisphere, who would not be able to correctly Interpret non-verbal cues. People who just use the right hemisphere may even interpret more accurately than people who use both hemispheres, because they are not questioning the content so much with the left hemisphere.
Finally, experiments with frogs and other animals of prey have shown that when the predator approaches from the left side, the frog jumps more quickly (due to the right side of hemisphere being activated from the environmental stimuli). If the snake/predator approaches from the right, the toad doesn’t respond as quickly (left side of hemisphere is activated). This is all because the frog must estimate the novelty/danger of the stimulus (right hemisphere). It must also determine whether the stimulus fits some familiar category, such as the predator category, in order to make the appropriate well-established response (left hemisphere). Humans go through a similar process of evaluating stimuli.
