The theory proposed in the late 1970s and early 1980s by Jeffrey Gray postulates that people differ in how sensitive they are to rewards and punishments. It is one of the major theories of personality proposing that three systems called behavioral activation system, behavioral inhibition system, and the fight-flight-or-freeze systems determine a wide range of human behavior.

Green spaces refer to areas within urban or rural environments that are primarily covered by vegetation, such as parks, gardens, forests, and natural reserves. These spaces provide numerous environmental, social, and economic benefits, including biodiversity conservation, air and water purification, recreational opportunities, and mental health benefits.

A short-hand way of referring to the gastrointestinal system. In this course, this term most commonly refers to the large intestine and the microbiota inhabiting it.

Dysbiosis is an imbalance in the normal composition and diversity of microorganisms within the gut, which can affect physical health, mental health, and various bodily functions.

Gut microbiota is a complex community of microorganisms residing in the digestive tract. It plays a crucial role in digestion, nutrient absorption, immune function, and mental health. A diverse and balanced gut microbiota is associated with better overall health.

Gut microbiota composition refers to the specific types and proportions of microorganisms that comprise the community in the gut. The composition can vary from person to person, and it plays a crucial role in various physiological functions, including digestion, immune regulation, and even mental health.

Gut microbiota diversity refers to the variety of different microorganisms, including bacteria, viruses, fungi, and other microbes, present in the gastrointestinal tract. A diverse gut microbiota typically includes a wide range of microbial species, which is associated with better overall health.

The gut lumen is the hollow interior space inside the gastrointestinal tract (GIT), starting from the mouth and extending to the anus. It is the region of the GI tract where ingested food and liquids are mixed with digestive secretions and undergo chemical and mechanical digestion. The gut lumen is surrounded by the other parts of the intestinal wall: the mucosa, the submucosa, the muscularis, and the serosa. It is also home to diverse microbial species known as gut microbiota.

Gut peptides are small protein-like molecules released by the gut and are structurally composed of 36 amino acids. Gut peptides exert biological effects on various organs, including the brain and the gut. Examples include PYY, CCK, and GLP (Holzer et al., 2012).

Gut-associated lymphoid tissues are the gut’s largest mass of lymphoid tissues and immune cells (such as B and T-cells, neutrophils, mast cells, macrophages, and dendritic cells). GALT is critical in maintaining gut health and protecting it from potentially harmful pathogens (Ruth & Field, 2013