• Stress Response: Negative or stressful thoughts activate the hypothalamic-pituitary-adrenal (HPA) axis, releasing cortisol and other stress hormones. Chronic stress can suppress immune function, increase inflammation, and contribute to various health issues.
• Relaxation Response: Positive or calming thoughts can activate the parasympathetic nervous system, promoting relaxation, reducing blood pressure, and supporting healing processes.

The brain's ability to change and adapt in response to thoughts and experiences, known as neuroplasticity, demonstrates how our thoughts can shape our biology.

• Meditation and Mindfulness: Practices like meditation can lead to structural changes in the brain, such as increased gray matter in areas associated with emotional regulation and decreased activity in the amygdala (stress response center).
• Positive Thinking: Positive thoughts and attitudes have been linked to better mental health and even enhanced physical recovery, such as faster healing after surgery.

This field studies the interactions between psychological processes, the nervous system, and the immune system.

• Immune Function: Research shows that positive emotions, social connections, and optimism can boost immune function, while chronic stress or depression can weaken it.
• Placebo Effect: Belief in a treatment's efficacy, even if it's a placebo, can lead to measurable physiological changes, such as pain relief or improved symptoms.

Epigenetics examines how lifestyle and environmental factors, including mental states, influence gene expression without altering DNA sequences.

• Thoughts and Gene Expression: Stress and negative thoughts can affect gene expression by increasing inflammatory markers, while positive states and practices like meditation can enhance genes associated with repair and resilience.
• Telomere Health: Chronic stress and pessimistic thinking are associated with shorter telomeres (protective caps on chromosomes), which are linked to aging and disease. Conversely, mindfulness and positive thinking can preserve telomere length.