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The other brains (the gut and heart)
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Document about the other brains in the human body - Gut, heart.
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The “Other” BrainsKey Words:
o Prebiotics = a specific fibre that acts as a stabiliser for good bacteria in the gut.
o Probiotics = living bacteria in the gut.
o Heart rate variability = the variation in the time interval between consecutive
heartbeats, in milliseconds.
o Coherence = a balanced state that is typically characterised by feeling content,
happy, in control and in sync within yourself and others.
o Baroreflex = rapid negative feedback loop mechanisms that help to maintain blood
pressure at nearly constant levels.
o Heart = a muscular organ with an autonomous nervous system.
o Afferent = conducted towards something, afferent neurons are sensory neurons that
carry signals from the stimulus to the brain and spinal cord.
o Enteric = relating to/occurring in the intestines.
Key Studies:
Rhee et al (2009): the mechanisms underlying the gut-brain-axis communications
involve neuro-immuno-endocrine mediators.
Tillisch et al (2013): probiotic bacteria in fermented milk were shown to reduce brain
activity in emotional centres, in healthy individuals = has a direct impact on how we
process emotions.
Mohamed et al (2019): probiotic supplements reduce symptom severity,
rehospitalisation rates and showed cognitive improvement in individuals with
schizophrenia and bipolar disorder.
Naveed et al (2021): modulation of the gut-brain axis may play a critical role in the
development of neuropsychiatric disorders such as: anxiety, depression,
schizophrenia, bipolar disorder, chronic pain and neurodevelopmental disorders e.g.,
ADHD, ASD.
Babo-Rebelo et al (2016): heartbeat evoked responses in the prefrontal cortex and
ventromedial prefrontal cortex varied depending on whether the participant was
thinking about themself or an external object/event = brain responds differently if
the information is coming from the heart/about self = brain uses heart as a self-
reference (self-directed thoughts).
Tallon-Baudry et al (2018): heartbeat evoked responses in the default network
(medial prefrontal cortex and cingulate cortex) during a warning interval were larger
in the hits than misses = neural responses to heartbeats before the stimulus could
predict whether a faint stimulus will be perceived or missed = relies on the idea that
attention and consciousness correspond to neural mechanisms (Visual perception).
Bradley et al (2010): students practiced self-regulation for 3months, afterwards =
resting HRV was significantly increased and the patten was more coherent, the
improvements were correlated with improved test scores and behaviours.
, - wary of these studies as it’s often the companies that offer self-regulation tools
that fund the study.
O’Rourke et al (2017): after delivering HRV biofeedback training to cancer survivors
they had reduced pain, fatigue, stress and depression.
Deschodt-Arsac et al (2018): short sessions of HRV biofeedback training in students
for 5 weeks = benefits to anxiety levels and the effects persisted for 12 weeks.
Shaffer et al (2014): afferent neuronal activity inhibits or facilitates synchronisation
of global cortical activity.
McCraty & Zayas (2014): afferents have connections to numerous brain centres
including: nucleus tractus solitarius, cortical areas, hypothalamus, amygdala,
periaqueducta gray.
Forte et al (2019): review to analyse the relationship between heart rate variability
and cognitive functions. Increased sympathetic activity and decreased
parasympathetic activity is associated with worse performance in some cognitive
domains, in the absence of dementia and severe cardiovascular diseases or other
medical and psychiatric disorders = highlights the influence of the autonomic
nervous system on cognitive functions but there are very few studies in this area so
need more but HRV could be considered as an early biomarker of cognitive
impairment in populations without dementia or stroke.
Naveed et al (2021): review, gut microbiota interacts with the brain, this modulation
can play a critical role in the pathology of neuropsychiatric disorders. Prebiotics,
probiotics and specific diets could be a promising therapeutic avenue for
neuropsychiatric disorders.
Notes:
The vagus nerve:
10th cranial nerve, CNX.
Interfaces with parasympathetic control of the heart, lungs and digestive tract.
Longest nerve of the autonomic nervous system.
80% of the fibres in the vagus nerve are afferent
Cameron (2002) and Bonaz et al (2018).
Vagus nerve stimulation as a gateway to interoception:
Interoception refers to the body to brain communication of: internal signals, sensing,
encoding and representation in the brain (Paciorek & Skora, 2020).
Hypothalamic pituitary adrenal (HPA) axis:
Hypothalamus releases cortisol, in a stressful situation = autonomic nervous system.
Hypothalamus is stimulated by the sympathetic nervous system which releases a
hormone called corticotrophin releasing factor (CRF) which activates the pituitary
gland, releasing adrenocorticotrophic hormone (ACTH). This alerts the adrenal
glands and stimulates the adrenal cortex to release cortisol and neuronstimulate. It
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