Neurobiology of Anxiety

ANXIETY is the central bond in the chain that links Fears and Phobias and is the emotion which you feel when your body is preparing itself to respond to some form of perceived threat

Neuro-biology studies the processes involving nerves which underpin how we behave, learn, perceive and store our experiences of the world around us. In particular it investigates every aspect of how the Brain operates.

” The mind is …what the Brain does” !

The most obvious tangible symptoms of anxiety are caused by the release of Adrenaline and then Cortisol from the Adrenal glands on top of the kidneys) and the effects which they have on the whole body system.

This will be considered in two  sections for convenience of healthcare professionals or anybody wanting a more detailed look;

• Neurobiology of the fear response, (‘flight and fight’) – Acute anxiety, Panic Attacks
• Neurobiology of Chronic Stress (and Burnout)

It is the Brain that is the director of the system that controls the release of these chemical messengers, evolved over evolution to respond to life-threatening threats to survival by triggering the ‘fight or fight’ response.

The Brain is best understood by considering it to be constructed of three main regions in line with its evolution since the appearance on earth of vertebrates and then mammals.

The Brainstem is the seat of our vital functions and operates to keep all the systems in the body in equilibrium (homeostasis). It evolved 200 million years ago and functions little differently to that of a lizard!

The Limbic system is the seat of all our emotional responses especially fear and aggression and our primitive responses to threat It is the kernel of the brain, evolved around 50 million years ago and is similar to a rat’s!

The Cerebral Cortex is the seat of our thinking, reasoning, language and awareness and our human characteristics. Whilst the size of the Limbic system remained roughly constant, the cerebral cortex expanded as our species evolved into primates. Apes walked upright around a million years ago, Homo Sapiens appeared only 200,000 years ago. A speck in time! Man lived in caves until only 13,000 years ago and societies less than 5000 years ago.

In essence the Brain can be considered to be a ‘chimps brain’ overlaying a ‘rat brain’ and supported by a ‘lizard brain’!

The Limbic system has connections to the cortex and brain stem and includes; the Hippocampus for memory and a physical link to the Pituitary gland (sends chemical messengers to The Adrenal gland).

The most important of all is the walnut-size structure, the Amygdala –the ‘fear’ centre of the brain.

The Amygdala is closely connected to the key brain components of perception, the way we take in information and respond to it. It is intimately linked to the adjoining Hippocampus, where memory of experienced events, facts and emotional context is stored.

The Amygdala is also closely connected to the Thalamus, the main relay centre between the cerebral cortex and many regions, particularly for sensory information as well as those regulating sleep and the perception of consciousness.

The structures of this system evolved to respond to life-threatening situations. Sensory information is processed, leading to cognitive understanding and the appropriate response -Flight, Fight or Freeze.

Many body systems and functions are affected by the actions of Adrenaline and Cortisol using three main pathways;

• ‘Motorway Route’ with a ‘fast lane’ and ‘slow lane’
• ‘Scenic‘ or ‘thoughtful’ route.

The ‘Motorway Route – Fast Lane’ (SAMS)

The Amydala processes incoming information from our sensory system. If it interprets this as a ‘threat’ then it responds immediately. The fastest route is via the nerve fibres of the spinal cord and the Sympathetic Nervous System.

Multiple organs; Skin, Heart, Lungs, Stomach, Kidneys are stimulated immediately. In particular the Medulla (inner core) of the Adrenal Gland which releases Adrenaline and Noradrenaline.

This is the basis for the physical manifestations of the ‘Fight and Flight response.

EYES: Dilate

SALIVARY GLANDS:  Inhibited

HEART: Beats faster and stronger

LUNGS: Bronchial tubes dilate

STOMACH: Digestion Inhibited

INTESTINE: Functions Inhibited

ADRENAL GLANDS: Stimulated

BLADDER: Relaxes

The Motorway Route – Slow Lane (HPA)

Simultaneously, on interpreting ‘threat’, the Amygdala stimulates a slower response via the blood stream.

This is known as the HPA Axis or the ‘Slow’ lane as it utilises the bloodstream.

AMYGDALA – receives sensory information and also is under ‘top down influences from other cerebral networks.

The Amygdala stimulates the Hypothalamus which in turn simulates the Pituitary Gland. The hormones released from the Pituitary Gland then stimulates the Adrenal Gland to produce the powerful hormone Cortisol.

Incoming information is processed not only by the Amygdala and distributed by the Thalamus. Neural networks in the cerebral cortex are in a constant state of readiness to receive, analyse and shape signals.  There are several areas involved, chief amongst them, the Pre-Frontal Cortex. The effect of this ‘thoughtful process’ is to exert an influence on the understanding and behaviour which results from the input.

When the perceptual system in the Brain interprets information as ‘life-threatening’ the Amygdala initiates the ‘Fast Lane’ response, SAMS. Multiple organs are stimulated by the Sympathetic Nervous system and ADRENALINE is produced.

This produces the ‘fight and flight response and the ‘Panic’ symptoms of Acute Anxiety Disorder and also of Phobias.

At the same time the ‘Slow Lane’ HPA system stimulates the release of ‘CORTISOL’. Unlike adrenaline, CORTISOL penetrates the blood-brain barrier.