Psychobiotics

Psychobiotics treat neurological disorders, including mild cognitive impairment (MCI) and Alzheimer's Disease. However, the mechanisms underlying their neuroprotective effects remain unclear.
Zhu et al. 2021d Nutrients 13: 1602

Psychobiotics are a special class of probiotics, which deliver mental health benefits to individuals. They differ from conventional probiotics in their ability to produce or stimulate the production of neurotransmitters , short-chain fatty acids , enteroendocrine hormones and Anti-inflammatory cytokines. Synbiotics that include a combination of bacteria providing mental health advantages, together with their complementary prebiotics, are classified as psychobiotics, too.
Sharma et al. 2021d Current Microbiology 78: 449–463

Research on prebiotics, although limited, shows that they can increase levels of BNDF (Brain-derived neurotrophic factor) and NMDA receptor (NMDAR) in the brain. This leads to better learning and memory in rodents.
Sharma et al. 2021d Current Microbiology 78: 449–463

“Psychobiotics,” a term coined by neuropharmacologist John Cryan and psychiatrist Ted Dinan, both at University College Cork.
Pennisi 2020 Science 368: 570-573

Although Probiotic Bacteria Will Be Concentrated after Ingestion, Mainly in the Intestinal Epithelium (where They Provide the Host with Essential Nutrients and Modulation of the Immune System), They May also Produce Neuroactive Substances Which Act on the Brain-gut Axis
Bermúdez-Humarán et al. 2019 Nutrients 11: 890

Psychobiotics release neuroactive substances directly influencing the human brain, psyche, and behavior
Oleskin & Shenderov 2019 Probiotics and Antimicrobial Proteins 11: 1071-1085

Researchers have looked at different prebiotic, and they found that fructooligosaccharides (FOS) and galactooligosaccharides (GOS) can help Bifidobacterium and Lactobacillus grow.
Estrada et al. 2001 Can J Anim Sci 81(1): 141-148
Bermúdez-Humarán et al. 2019 Nutrients 11(4): 890

Prebiotics, as suggested by Sarkar et al., can be considered part of the definition of psychobiotics. They aid in the growth of bacteria with psychobiotic potential, thereby contributing to the enhancement of mental health. Recently, the meaning of psychobiotics has been broadened. It now includes supplements, exercise, antibiotics, and antipsychotics. These can change the gut environment indirectly and help psychobiotic bacteria.
Sarkar et al. 2016 Trends Neurosci 39(11): 763-781

Psychobiotics are a subclass of probiotics that have a range of effects, from enhancing mood to aiding in neural development. According to Dinan et al., psychobiotics are defined as living organisms that, when consumed in sufficient quantities, provide health benefits to individuals with psychiatric or neurological conditions.
Dinan et al. 2013 Biol Psychiatry 74(10): 720-726

see also:
Gut microbiota & Tryptophan metabolites