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The Role of Neurotransmitters in Mental Health

Publication date: 17 December 2011

Mainstream medicine views mental and neurological disorders in terms of neurochemical imbalances, and attempts to correct these using medications. For example depression is seen as a serotonin imbalance, and the most common class of anti-depressants (SSRIs) target the serotonin network. Whether or not depression really is a serotonin imbalance is a matter of controversy, but at least we can agree it would be a step forward if we had a means of objectively assessing the individual's serotonin status, or the likelihood of SSRIs actually working (they don't work for everybody). At present there is no reliable lab test that can do this. Of course there's a lot more to optimal brain functioning than chemistry, but it does seem to be an important part of the whole.

In my last post I mentioned the work of Dr Dan Amen, a neuropsychiatrist who uses SPECT brain imaging to classify his patients' varieties of depression, anxiety, ADHD. His classification is then the basis for his choice of treatment (not just medications but natural therapies too).

This seems like a real step forward to me. Can EEG assessment be used in a similar way – as a sort of poor man's SPECT scan? There certainly seems to be the potential – indeed Dr Amen used EEG before moving to SPECT.

The value of any assessment is in directing the choice of therapy. In my case I'd like to use EEG assessment to help me select nutritional supplements that will affect brain biochemistry. First we need to attempt to relate EEG patterns to neurochemistry. So that's the topic of this post. And I need to begin with an overview of the main class of neurochemicals – neurotransmitters.

What Is A Neurotransmitter?

A neurotransmitter is a substance that carries a message between brain cells (neurons). Neurotransmitter molecules are secreted by one neuron and detected by receptors in adjacent neurons. Mostly this happens at junctions between cells called synapses. Neurotransmitters can be excitatory, meaning they stimulate greater activation of the receiving neurons, or inhibitory, meaning they dampen down activation. Imbalances in neurotransmitters manifest as symptoms. Imbalances can be created by there being literally too much or too little neurotransmitter, but also by a problem with the receptors, or a problem with the brain's mechanisms for mopping up neurotransmitters after they've done their job.

The brain's main excitatory neurotransmitter is glutamate. In some disorders it appears there is an excess of glutamate, and this causes problems. Examples are Parkinson's and possibly bipolar disorder. In the extreme case glutamate becomes toxic and can kill neurons (a process called excitotoxicity). Symptoms associated with excess glutamate are explosive emotions such as anger, rage, aggression and panic, also hyperactivity, migraines, insomnia, irritability and poor concentration, and perhaps mania.

The brain's main inhibitory neurotransmitter is GABA. A lack of GABA is associated with anxiety. Many drugs that counter anxiety (anxiolytics) do so by stimulating GABA release. Because GABA has the opposite effect of glutamate, there's a lot of overlap between glutamate excess and GABA deficit.

Neuromodulators

An important sub-class of neurotransmitters are the neuromodulators, the main ones being serotonin, dopamine, noradrenalin and acetylcholine. They differ in that rather than directly carrying information, they affect the way cells respond to information. If the song playing on your stereo is glutamate and GABA, then the neuromodulators are like the volume, bass and treble controls. On the whole they seem to induce greater activation in the brain.

Dopamine is associated with drive and motivation. The brain secretes dopamine as a kind of reward signal, meaning we tend to want more of what just happened. Many addictive drugs such as cocaine stimulate dopamine.

It's thought that several disorders are associated with dopamine deficit – including ADHD, addiction, and a variety of depression typified by emotional flatness and lack of motivation.

Dopamine stimulates the frontal part of the brain, especially the prefrontal cortex, a critical brain region for executive function – concentration / focus, planning and decision making, holding things in mind (short term memory) and emotional regulation. So it makes sense that the symptoms of dopamine deficit are distractability, low drive and motivation, and emotional flatness.

Serotonin is associated with mood – in particular serotonin deficit is linked to depression. Drugs that block the action of serotonin induce low mood, as does removing from the diet the nutritional building blocks of serotonin. The serotonin-deficient variety of depression is characterised more by feelings of misery as opposed to flatness and lack of drive (the dopamine variety). Serotonin is also associated with wakefulness and its dysregulation with sleep disturbance. (Dopamine deficit can also affect sleep but in this case sleep seems to be excessive and unrefreshing.) OCD and some eating disorders also seem to be related to serotonin.

Serotonin releasing neurons stimulate much of the brain.

Noradrenalin (also known as norepinephrine) is associated with arousal and vigilance. Experiments suggest noradrenalin is released when something new happens, that alerts our interest. So like dopamine, noradrenalin is also associated with attention, concentration, short term memory and other executive functions. So as you might expect, the major symptom associated with noradrenalin deficit is poor concentration and poor cognitive functioning. Like serotonin, noradrenalin secreting neurons stimulate all parts of the brain, and are associated with wakefulness.

Chemically, noradrenalin is derived from dopamine. Nutrients that support the dopamine pathway, also support noradrenalin production.

Less is known about acetylcholine's function in the brain, which appears complex, but it is connected to memory. It's particularly prevalent in the hippocampus, a brain sructure critical to memory. Acetylcholine producing neurons are among the first to die in Alzheimer's which of course affects memory.

It remains for me to relate neurotransmitters to EEG findings – but this post has grown so long that I hope you'll forgive me if I delay this till my next post – coming soon.

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