Homeostasis, or Why Is Dieting So Hard?
In a neurological context, homeostasis is the maintenance of a stable internal environment by detecting changes and coordinating responses to keep vital signs like temperature, blood pressure, and blood glucose levels within a narrow, functional range. The nervous system uses feedback loops to achieve this: it receives information from sensory receptors, processes it in a control center (often the brain), and sends signals to effectors (like muscles and glands) to counteract any deviation from a set point
The main control center for homeostasis in the brain is hypothalamus, a small but vital structure located deep within the brain. The hypothalamus acts as the body's thermostat and coordinates functions like body temperature, hunger, thirst, sleep, and hormone release to maintain a stable internal environment.
Hypothalamus: This region receives information from the body's sensors and the autonomic nervous system to regulate various internal functions. It helps control body temperature, sleep-wake cycles, and the release of hormones.
Other contributing areas: While the hypothalamus is the primary regulator, other brain areas are involved. The medulla oblongata, located in the brainstem, is a center for autonomic reflexes essential for homeostasis, such as regulating blood pressure and heart rate. The brain also uses specialized neuronal networks in regions like the arcuate nucleus (ARC) within the hypothalamus to sense metabolic signals and regulate energy balance.
https://www.sciencedirect.com/topics/neuroscience/medulla-oblongata
Neurological Basis for the Hedonic Principle
What part of the brain is hedonic?
As experiences of pleasure (euphoria) and displeasure (dysphoria), hedonics are omnipresent in daily life. As core processes, hedonics accompany emotions, motivation, bodily states, etc. Orbitofrontal cortex and nucleus accumbens appear to be hedonic brain hubs.
For this class, let us focus on the problems of dysphoria.
https://www.sciencedirect.com/topics/neuroscience/dysphoria
With respect to brain structure and function, Dysphoria is associated with dysfunction in several key brain regions, including the prefrontal cortex, amygdala, hippocampus, anterior cingulate cortex, and reward circuitry centered on the ventral tegmental area (VTA) and nucleus accumbens. The VTA–nucleus accumbens pathway is implicated in reward processing, and impaired function in this circuit is thought to mediate dysphoria. The anterior cingulate cortex is involved in affective control, and its dysfunction might be related to affective dysregulation characteristic of certain disorders.
The Neurological Basis of Hunger
https://digitaleditions.library.dal.ca/intropsychneuro/chapter/hunger-and-eating/
The hypothalamus (located in the lower, central part of the brain) plays a very important role in eating behaviour. It is responsible for synthesizing and secreting various hormones. The lateral hypothalamus (LH) is concerned largely with hunger and, in fact, lesions (i.e., damage) of the LH can eliminate the desire for eating entirely—to the point that animals starve themselves to death unless kept alive by force feeding (Anand & Brobeck, 1951). Additionally, artificially stimulating the LH, using electrical currents, can generate eating behaviour if food is available (Andersson, 1951).
Hunger is only part of the story of when and why we eat. A related process, satiation, refers to the decline of hunger and the eventual termination of eating behaviour. Whereas the feeling of hunger gets you to start eating, the feeling of satiation gets you to stop. Perhaps surprisingly, hunger and satiation are two distinct processes, controlled by different circuits in the brain and triggered by different cues. Distinct from the LH, which plays an important role in hunger, the ventromedial hypothalamus (VMH) plays an important role in satiety (more on this in the tricky topic below). Though lesions of the VMH can cause an animal to overeat to the point of obesity, the relationship between the LH and the VMB is quite complicated.
The physical sensation of hunger comes from contractions of the stomach muscles. These contractions are believed to be triggered by high concentrations of the hormone ghrelin. Two other hormones, peptide YY and leptin, cause the physical sensations of being full. Ghrelin is released if blood sugar levels get low, a condition that can result from going long periods without eating.
The vagus nerve acts as a direct line of communication between the brain and the enteric nervous system (ENS), the "second brain" of the gut. It relays sensory information about gut conditions to the brain and sends motor commands from the brain to the gut to regulate digestive processes like nutrient absorption, acid secretion, and muscle contractions. This bidirectional connection is crucial for maintaining gut health, regulating mood and energy, and controlling immune responses.
Let's review the working of Ozempic, given this new information.
Ozempic influences digestion by activating GLP-1 receptors, which slow stomach emptying and intestinal movement. It directly affects the vagus nerve, a key component of the parasympathetic nervous system that regulates digestion.
Ozempic affects the gut (stomach) by delaying gastric emptying. This keeps food in your stomach longer, slows down digestion and can make you feel bloated. This is a direct action on the enteric nervous system.
Not done yet! Cholecystokinin (CCK) is a hormone produced in the small intestine that regulates digestion, particularly after eating fats and proteins. It signals the gallbladder and pancreas to release bile and enzymes, respectively, into the small intestine to help break down food. CCK also plays a role in the brain, affecting satiety and potentially influencing anxiety.
Hormones can have a wide range of effects on hunger. The hormones insulin and cholecystokinin (CCK) are released from the GI tract during food absorption and act to suppress feelings of hunger. However, during fasting, glucagon and epinephrine levels rise and stimulate hunger. When blood sugar levels fall, the hypothalamus is stimulated. Ghrelin, a hormone produced by the stomach, triggers the release of orexin from the hypothalamus, signalling to the body that it is hungry.
The Neurological Basis of Sexual Motivation
https://fiveable.me/physiology-motivated-behaviors/unit-7/neural-mechanisms-sexual-motivation-arousal/study-guide/KCdJXFwu0iAMEsfv
Sexual motivation and arousal involve complex neural mechanisms. The hypothalamus and limbic system play key roles, with hormones and neurotransmitters influencing behavior. Specific brain regions like the medial preoptic area and ventromedial nucleus regulate different aspects of sexual function.
Understanding these neural mechanisms helps explain sexual behaviors and dysfunctions. Hormones like testosterone and estrogen act on the brain to modulate arousal, while neurotransmitters like dopamine enhance motivation. This knowledge informs treatments for sexual disorders and our understanding of sexual orientation.
Hypothalamus regulates sexual behavior through medial preoptic area (MPOA) and ventromedial nucleus (VMN)
MPOA crucial for male sexual behavior (mounting, intromission, ejaculation)
VMN essential for female sexual receptivity and proceptivity
Limbic system processes emotional and contextual cues related to sexual behavior
Amygdala involved in emotional processing of sexual stimuli
Hippocampus contributes to contextual memory formation during sexual experiences
Hormonal and Neurotransmitter Influences
Gonadal hormones act on specific brain regions to modulate sexual motivation and arousal
Testosterone primary hormone in males
Estrogen and progesterone key hormones in females
Neurotransmitters mediate various aspects of sexual behavior
Dopamine enhances sexual motivation and pleasure (nucleus accumbens, ventral tegmental area)
Serotonin generally inhibits sexual behavior (raphe nuclei)
Oxytocin promotes bonding and facilitates orgasm (paraventricular nucleus of hypothalamus)
Autonomic nervous system regulates physiological responses during sexual arousal
Sympathetic activation increases heart rate and blood pressure
Parasympathetic activation causes genital vasocongestion (erection in males, lubrication in females)
Cognitive factors interact with neural mechanisms to influence sexual motivation and arousal
Attention modulates processing of sexual stimuli (prefrontal cortex)
Memory influences sexual expectations and experiences (hippocampus)
Anticipation and reward prediction affect sexual motivation (ventral striatum)
Testosterone and estrogen act as primary regulators of sexual behavior
Hormones influence gene expression in specific brain regions
Organizational effects occur during development (permanent changes)
Activational effects occur in adulthood (temporary changes)
Testosterone and its metabolites modulate sexual motivation and performance
Estradiol (aromatized testosterone) crucial for male sexual behavior
Dihydrotestosterone (DHT) important for male genital development
Estrogen, particularly estradiol, plays a key role in female sexual behavior
Influences receptivity (lordosis behavior in rodents)
Affects proceptivity (solicitation behaviors)
But here is where things get tricky. Schacter (2023) is clear on the next point:
Testosterone primarily affects female sexual behavior by
influencing libido, or sex drive, particularly in women with low levels. Studies show that testosterone can increase sexual desire, arousal, and genital sensations, though the effects can be influenced by other hormones like estrogen and are most noticeable in women with lower testosterone levels, such as those experiencing menopause. It's also linked to a woman's attraction to masculine traits in men, which can fluctuate with her testosterone levels during the menstrual cycle.
Hormones interact with neurotransmitter systems to modulate sexual motivation and arousal
Testosterone enhances dopamine release in mesolimbic system
Estrogen modulates serotonin receptor expression
Hypothalamic-pituitary-gonadal (HPG) axis regulates sex hormone production and release
Gonadotropin-releasing hormone (GnRH) from hypothalamus stimulates pituitary
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from pituitary act on gonads
Negative feedback loop regulates hormone levels
Non-gonadal hormones contribute to sexual and social bonding behaviors
Oxytocin promotes pair bonding and facilitates orgasm
Vasopressin involved in male-typical social behaviors and pair bonding
Sex Differences in Neural Mechanisms of Sexual Behavior
Sexually dimorphic nucleus of the preoptic area (SDN-POA) larger in males
Influences male-typical sexual behaviors (mounting, intromission)
Size difference established during prenatal development
Ventromedial hypothalamus (VMH) crucial for female sexual receptivity
Higher density of estrogen receptors in females
Estrogen action in VMH facilitates lordosis behavior
Medial amygdala shows sex-specific activation patterns during sexual behavior
Greater activation in males during mating
Processes pheromonal and olfactory cues differently in males and females
Testosterone acts primarily through androgen receptors in males
Maintains male sexual motivation and performance
Supports spermatogenesis and secondary sexual characteristics
Testosterone often converted to estradiol in females to influence sexual behavior
Aromatase enzyme converts testosterone to estradiol in brain
Estradiol acts on estrogen receptors to modulate female sexual behavior
Sex differences in neurotransmitter systems contribute to behavioral variations
Serotonergic system more sensitive to estrogen in females
Dopaminergic system shows sex-specific responses to sexual stimuli
Neural circuits involved in sexual motivation and arousal show plasticity
Can be influenced by hormonal and environmental factors differently in males and females
Experience-dependent changes in synaptic connections and neurotransmitter release
Cognitive and emotional processing of sexual cues may differ between sexes
Reflects both biological predispositions and sociocultural influences
Contributes to differences in sexual arousal patterns and partner preferences
Impact of Neurotransmitters on Sexual Motivation and Arousal
Dopamine plays crucial role in sexual motivation, reward, and reinforcement
Increased activity in mesolimbic dopamine system during sexual arousal and orgasm
Dopamine release in nucleus accumbens associated with sexual pleasure
Norepinephrine contributes to sexual arousal
Contributes to differences in sexual arousal patterns and partner preferences
Enhances attention to sexual stimuli
Facilitates physiological responses (increased heart rate, blood pressure)
Glutamate modulates sexual behavior by influencing neuronal excitability
Acts on NMDA and AMPA receptors in key brain regions
Involved in synaptic plasticity related to sexual learning and memory
Serotonin generally inhibits sexual behavior
Increased levels associated with decreased libido and sexual function
Selective serotonin reuptake inhibitors (SSRIs) can cause sexual side effects
Gamma-aminobutyric acid (GABA) modulates sexual behavior
Reduces anxiety and inhibition, potentially facilitating sexual activity
Interacts with other neurotransmitter systems to regulate sexual arousal
Endogenous opioids contribute to pleasurable sensations during sexual activity
Endorphins released during orgasm produce euphoria and pain reduction
Opioid system involved in sexual reward and reinforcement
Neuropeptides and Hormones
Oxytocin promotes bonding, trust, and intimacy
Released in large amounts during orgasm
Facilitates pair bonding and maternal behaviors
Vasopressin contributes to male-typical social and sexual behaviors
Involved in partner preference and territorial behaviors
Interacts with dopamine system to reinforce pair bonding
Neural Basis of Sexual Orientation and Gender Identity
Sexually dimorphic nucleus of the preoptic area (SDN-POA) shows variations related to sexual orientation
Size and cell number may differ between heterosexual and homosexual individuals
Influenced by prenatal hormone exposure
Bed nucleus of the stria terminalis (BNST) implicated in gender identity
Structure and function more closely resemble identified gender in transgender individuals
Involved in processing of emotional and sexual information
Neuroimaging studies reveal differences associated with sexual orientation
Variations in amygdala response to sexual stimuli
Differences in hypothalamic activation patterns
Developmental and Hormonal Factors
Prenatal hormone exposure shapes neural circuits involved in sexual orientation and gender identity
Androgens play key role in masculinization of brain structures
Variations in hormone levels or receptor sensitivity may influence development
Epigenetic mechanisms contribute to sexual orientation and gender identity development
Environmental factors can influence gene expression in the brain
Epigenetic changes may persist across generations
Neural circuits involved in sexual attraction and partner preference show plasticity
Can be influenced by both biological and environmental factors throughout life
Early experiences may shape neural pathways related to sexual preferences
Gender identity involves complex interplay between multiple brain regions
Areas associated with body perception (parietal lobe) and self-awareness (medial prefrontal cortex) implicated
Social and cultural factors interact with biological predispositions
Neural Basis of Acheivement Motivation
https://pubmed.ncbi.nlm.nih.gov/18550387/
We have used functional magnetic resonance imaging to study the neural correlates of motivation, concentrating on the motivation to learn and gain monetary rewards. We compared the activation in the brain obtained during reported high states of motivation for learning, with the ones observed when the motivation was based on monetary reward. Our results show that motivation to learn correlates with bilateral activity in the putamen, and that the higher the reported motivation, as derived from a questionnaire that each subject filled prior to scanning, the greater the change in the BOLD(blood oxygen dependent level) signals within the putamen. Monetary motivation also activated the putamen bilaterally, though the intensity of activity was not related to the monetary reward. We conclude that the putamen is critical for motivation in different domains and the extent of activity of the putamen may be pivotal to the motivation that drives academic achievement and thus academic successes.
Background Notes:
The putamen is a rounded structure located at the base of the forebrain, deep within the brain's cerebral hemispheres. . It is the most lateral part of the lentiform nucleus and is situated lateral to the globus pallidus and separated from the caudate nucleus and thalamus by the internal capsule.
How about failure due to procrastination?
https://pubmed.ncbi.nlm.nih.gov/34407664/
Here, we adopted the voxel-based morphometry (VBM) and resting-state functional connectivity (RSFC) methods to study this issue. The VBM analysis revealed that higher achievement motivation was correlated with larger gray matter volumes in left precuneus (lPre). Furthermore, the RSFC results showed that the functional connectivity between lPre and right anterior cingulate cortex (rACC) was positively associated with achievement motivation and negatively correlated with procrastination.
What is a voxel? That is the basic 'brick' of Minecraft.