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The Right Brain Hypothesis For Obesity (2)
- 1. Miguel Alonso-Alonso MD, MPhil Alvaro Pascual-Leone, MD, PhD Department of Neurology, Beth Israel Deaconess Medical Center and Harvard Medical School Boston, MA Vincent Lee, Matthew McAdams, Socheata Lao
Editor's Notes
- Evolutionary persepctive Most of Human history our struggle for life involved Seeking/consuming/storing food as a means of survival. Our brains and bodies adapted to thrive in these environmental conditions. Current scheme for hunger or appetite Under hypothalamic regulation/control One of the first brain regions to evolve Involved in many different functions for the human body. Hunger/thirst/blood pressure/body temperature/sleep wake cycles etc. Our bodies also adapted; since w e had to travel great distances to find food and evolved mechanisms to adjust for feeding and energy expenditure. Developed neuroendocrine circuits or pathways. Releasing Neurotransmitters (ACH/NE) and neuropepetides (i.e Leptin/insulin/ghrelin) Important to know there are many intricate pathways that are thought to control hunger. important to note from a evolutionary perspective Eating food to store energy is fundamental for our survival – thus we develop a biological system to store energy in our white adipose tissue. For most of human history, the struggle for life was about seeking/consuming and storing food, and our brains and bodies adapted to thrive in these environmental conditions. We had to travel great distances to find food and evolved mechanisms to adjust for feeding and Energy expenditure. Neuroendocrine circuits that control appetite Ensure adequate balance that matches bodily needs.
- However, there are other human evolved aspects of eating food. Not only just a means for survival But now evolved into a sophisticated behavior involving social (community gatherings to share food) Cultural (religious fasting or feasts) Eating food also has a hedonic aspect Not only for satiating appetite but also, it brings pleasure/gratification/stimulate reward and motivation activating limbic/paralimbic system releasing dopamines and endorphins into our bodies. Therefore, these human cognitive dimensions can override metabolic needs or palatability; and is critical in understanding the pathogenesis of obesity.
- Authors suggest; the prefrontal cortex is responsible for cognitive “thought process” control of food intake. implicated planning complex cognitive behaviors expression of personality conflict resolution (decision making) moderating correct social behavior Orchestrating of thoughts and actions in accordance with internal goals. Top down control Innate (automatic impulses due to familiarity) vs. intentions (executive functions) executive functions – ability to differentiate among conflicting thoughts, determine good and bad, better and best, same and different, future consequences of current activites, working toward a defined goal, prediction of outcomes, working toward a defined goal, prediction of outcomes expectation based on actions social control of unacceptable outcomes.
- Author’s present several compelling evidence that links the right Prefrontal cortex with obesity or overeating. Obese people have a decrease ability to Frontal Lobotomy Overeating and weight gain Damage to right frontal lobe Gourmand Syndrome Frontal lombotomy the frontal lobe connections are excised side effect was overeating/weight gain Damage to right prefrontal cortex induced a condition called Gourmand syndrome -post-injury individuals develop a passion for eating gourment fine food. Degenerative dementia cause hyperphagia in specifically cases with right frontal lobe injury Hypoperfusion of Right frontal lobe implications in overeating conditions such as Kleine-Levin syndrome sleepy-beauty syndrome – neurological disorder – characterized by recurring periods of excessive amounts of sleep and altered behavior. In some cases these individuals have food cravings. In contrast, hyperactivity of Right Prefrontal cortex cause anorexia like symptoms. General trend here, that dysfunction/damage to the specifically the right prefrontal lobe is linked to a change in behavior to overconsume more than normally.
- in prep for future food shortages. Degree of activation of Right PFC may determine degree of inhibition of downstream signals that promote overeating. Leading to obesity in industrialized societies Degree of activation of Right PFC may determine degree of inhibition of downstream signals that promote overeating.
- worldwide in relatively short period. Cortisol induced right PFC dysfunction Right PFC : dopaminergic projections display sensitivity to stressors. Social conflicts
- Due to prolonged hypothalamic-pituitary-adrenal axis Other factors Genetic inter-individual differences Social structures Cultural habits
- will increased intake of methyl donors lead to weight loss in humans?
- Several cortical areas including the pfc Homeostatic hypothalamic circuits Reward pathways Cortical areas involved in: behavioral food intake physical activity
- Athletes Enhanced right-hemispheric preference in motor and cognitive tasks. Exercise training Improves performance in PFC-related cognitive tasks Increase in right frontal lobe volume. Motor areas Drive to move Apathy Central fatigue Underlying sedentarism
- Author’s present several compelling evidence that links the right Prefrontal cortex with obesity or overeating. Frontal lombotomy the frontal lobe connections are excised side effect was overeating/weight gain Damage to right prefrontal cortex induced a condition called Gourmand syndrome -post-injury individuals develop a passion for eating gourment fine food. Degenerative dementia cause hyperphagia in specifically cases with right frontal lobe injury Hypoperfusion of Right frontal lobe implications in overeating conditions such as Kleine-Levin syndrome sleepy-beauty syndrome – neurological disorder – characterized by recurring periods of excessive amounts of sleep and altered behavior. In some cases these individuals have food cravings. In contrast, hyperactivity of Right Prefrontal cortex cause anorexia like symptoms. General trend here, that dysfunction/damage to the specifically the right prefrontal lobe is linked to a change in behavior to overconsume more than normally.
- The Right prefrontal cortex is also thought to control our moral cognition; consensus of manners and customs within a social group, or to an inclination to behave in some ways but not in others Helping to guide our decisions according to a higher level. Evidence: Disruption of right PFC Leads to risk taking- or disregarding the long term goals of an action. Inhibition of Right Dorsolateral PFC Ultimatum Game – economic game; where there is a sum of money between two people. One person decides on how to divide the sum and the other person either rejects or accepts it. If acceptance = win and get the money; if rejection = nobody wins. Decreases rejection rates of unfair offers. This suggest that the right PFC is significant in controlling our moral reasoning and fairness judgment in decision making. Right PFC bias in: suppression of self-oriented behaviors moral reasoning and fairness judgment in decision making. And that Right PFC dysfunction in relation to obese individuals may cause them to fail in appropriately weighing adverse consequences of indulging in bad diets. OR Disregard for long term adverse consequences of choices Also, it may be associated with poor compliance of obese individuals to commit to weight loss interventions. i.e. women with high BMI are associated with poor adherence to breast cancer screening; even though they are at the highest risk. Implications for control of food intake relevant: Industrialized societies Oversupply of food vs. health food conscious Social conduct Comprehension of bodily information
- Visuospatial information Perceptions of human body Self body image body image and facets of self i.e. 54 yr. old woman – dominant right frontal lobe dementia Other personality Fond of fast foods Overeater Socially inappropriate after consuming meal vs. non-dieters Lower level of bodily awareness “ weight estimate error” correlates directly with BMI Lack of embarassment