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Chronic Stress and Chronic Stress and ImpulsivityImpulsivity

Effect in ObesityEffect in Obesity

Imelda Medina, MD Imelda Medina, MD

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Chronic Stress

Impulsivity Food Intake

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Hypothalamic Pituitary Adrenal Hypothalamic Pituitary Adrenal AxisAxis

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Stress and biological responseStress and biological responseImpact of uncontrollability and social evaluative Impact of uncontrollability and social evaluative

elementselementsMeta-analysis review of 208 laboratory studies of acute psychological Meta-analysis review of 208 laboratory studies of acute psychological

stressorsstressorsDickerson SS and Kemeny ME 2004Dickerson SS and Kemeny ME 2004

Mean cortisol effect size for studies using cognitive tasks, publicspeaking/verbal interaction tasks, public speaking/cognitive combination tasks, noise exposure, and emotion induction. Public speaking/cognitive task combination yields the highest response.

Mean cortisol effect size for studies using passive tasks, motivated performancetasks, uncontrollable motivated performance tasks, motivated performance taskswith social-evaluative threat, and uncontrollable motivated performance taskswith social-evaluative threat.

Mean ACTH and cortisol effect sizes for motivated performance tasks with social-evaluative threatand uncontrolability and for tasks without bothcharacteristics (ACTH =white column; cortisol=darkcolumn).

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ImpulsivityImpulsivity

• Impulsivity, "a force that moves something along" is a Impulsivity, "a force that moves something along" is a personality trait which varies among individuals. Important for personality trait which varies among individuals. Important for normal behavior and adaptation.normal behavior and adaptation.

• Recent theories have decomposed impulsivity into 4 dimensions Recent theories have decomposed impulsivity into 4 dimensions which include urgency, lack of premeditation (the inability to which include urgency, lack of premeditation (the inability to anticipate consequences), lack of perseverance (the inability to anticipate consequences), lack of perseverance (the inability to stick to one's task) and Sensation-seeking (the experience stick to one's task) and Sensation-seeking (the experience positive feelings towards risky actions).positive feelings towards risky actions).

• Abnormal impulse control is central feature of multiple mental Abnormal impulse control is central feature of multiple mental health conditions.health conditions.

• Impulsivity has been shown to be positively related to food Impulsivity has been shown to be positively related to food intake.intake.

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Impulsivity-SignificanceImpulsivity-Significance

As stated in the DSM-IVAs stated in the DSM-IV

• Impulse control disorders include:Impulse control disorders include:ADHDADHD

Intermittent explosive disorder Intermittent explosive disorder KleptomaniaKleptomaniaPyromaniaPyromaniaPathological gambling Pathological gambling Trichotillomania Trichotillomania Impulse-control disorder not otherwise specifiedImpulse-control disorder not otherwise specified

• The following ocnditions may have features that involve problems of impulse The following ocnditions may have features that involve problems of impulse control:control: Substance-related disordersSubstance-related disorders

paraphilias paraphilias antisocial personality disorder antisocial personality disorder conduct disorderconduct disorderschizophreniaschizophreniamood disorders mood disorders

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Impulsivity-SignificanceImpulsivity-Significance

• The essential feature of Impulse-control disorders is the The essential feature of Impulse-control disorders is the failure to resist an impulsefailure to resist an impulse, drive, or temptation to , drive, or temptation to perform an act that is harmful to the person or to perform an act that is harmful to the person or to others. others.

• Usually, the individual feels an increasing sense of Usually, the individual feels an increasing sense of tension or arousal before committing the act and then tension or arousal before committing the act and then experiences pleasure, gratification, or relief at the time experiences pleasure, gratification, or relief at the time of committing the act. of committing the act.

• Following the act there may or may not be regret, self-Following the act there may or may not be regret, self-reproach, or guilt. reproach, or guilt.

• Excessive food intake has been positively linked with Excessive food intake has been positively linked with dysfunctional impulsivity.dysfunctional impulsivity.

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How does Chronic Stress How does Chronic Stress effects Impulsivity?effects Impulsivity?

• Pre-clinical and clinical studies have converged to show Pre-clinical and clinical studies have converged to show that monoaminergic neurotransmitter systems (eg. that monoaminergic neurotransmitter systems (eg. dopamine) and the cortico-striatal circuitry are essential to dopamine) and the cortico-striatal circuitry are essential to impulse control. Basically, most evidence points toward impulse control. Basically, most evidence points toward that that brain dopamine levels are inversely related to brain dopamine levels are inversely related to impulsivityimpulsivity. . Low activity dopamine statesLow activity dopamine states are positively are positively related to higher levels of impulsivity.related to higher levels of impulsivity.

• Pre-clinical and clinical evidence shows that chronic stress Pre-clinical and clinical evidence shows that chronic stress and resulting glucocorticoids affect the dopaminergic and resulting glucocorticoids affect the dopaminergic reward mesolimbic pathway. Chronic stress leads to a reward mesolimbic pathway. Chronic stress leads to a state of low dopamine activity in the brain and it has been state of low dopamine activity in the brain and it has been observed to increase impulsivity. One of the possible ways observed to increase impulsivity. One of the possible ways is through its effect on dopaminergic neurons degeneration. is through its effect on dopaminergic neurons degeneration.

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Dopamine Hypothesis of Dopamine Hypothesis of RewardReward• Postulates that the actions of drugs of Postulates that the actions of drugs of

abuse are rewarding as a consequence abuse are rewarding as a consequence of activation of dopamine in the of activation of dopamine in the mesolimbic dopamine system. mesolimbic dopamine system.

• A similar mechanism occurs with A similar mechanism occurs with amphetamine, cocaine, nicotine and amphetamine, cocaine, nicotine and food. food.

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Obesity and Brain RewardObesity and Brain Reward

Human dopamine projections: (1) The nigrostriatal projection, which is concerned with movement .(2) and (3) The mesolimbic dopamine projection, which is involved in reward-related functions.

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Dopamine receptors and Dopamine receptors and obesity obesity

(a) The upper pair of images show dopamine receptor availability in control and obese participants. Note the clear difference between them. The lower pair of images show brain metabolic activity. Note that there is no difference between them.

(b) The relationship between brain dopamine receptor availability and the degree of obesity.

(Want GJ, Volkow ND et al 2001; Volkow ND and Wise RA 2005)

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What is the relationship What is the relationship between Dopamine and between Dopamine and

Obesity?Obesity?• Obesity SongObesity Song

– ““What if you lack a What if you lack a dopamine receptor, dopamine receptor, that would hold back that would hold back the feeling of the feeling of rapture, and here is rapture, and here is the case about the case about dopamine secretion, dopamine secretion, you are more you are more receptive to an obese receptive to an obese transformation”.transformation”.

• http://http://www.youtube.com/www.youtube.com/watch?watch?v=bEfcwltXZ2Qv=bEfcwltXZ2Q