Why so Afraid, Little Flower? Is it your Amygdala Again?

We are all at the mercy of our genes. Your genes determine the color of your eyes, your hair, your approximate height, and much of your personality. Are you sanguine? Are you cheerful? Are you fearful? Activation of your amygdalae has a lot to do with serotonin levels in synapses, and the level of negative emotions you experience. Serotonin levels in the synapse are largely determined by your genes. "How Genes Make up Your Mind" is an interesting article in the Science and Consciousness Review.

Genes control the development of neurons to make up brains, but they also govern neuronal gene expression during our daily lives. The sleep-waking cycle is controlled by neurochemicals emerging from cells at the base of the brain. Genes control how neurons communicate with serotonin, dopamine or other neurotransmitters (cache). Genes are responsible for every step of the neurotransmitter cycle, including the formation, transport, pre-synaptic expression and post-synaptic reception of the transmitter (see Figure 1). Genes work at every level of the neural process. They are the fundamental building blocks for both the structure and the functioning of the brain.

....How do genes influence the emotional workings of brains? Recent studies now show that naturally occurring genetic variations - called polymorphisms (cache) - which code for serotonin affects our emotional reactions and thoughts. Humans have two common variations of a promoter region of the serotonin transporter gene (5-HTTLPR); a short (s) and a long (l) version. It has been shown that two allelic (cache) copies of the long variant leads to higher concentration of 5-HTT mRNA, which leads to a doubled reuptake of serotonin, compared to one or two short allelic variations. People who have two copies of the long genetic sequence in this region have less serotonin available in the synapse, due to the higher reuptake of the neurotransmitter.

....The researchers found that the actvation of the two amygdalas differed between the two groups (see Figure 4). The s group showed a significantly higher amygdala activation than the l group. In other words, the level of amygdala activation depended on what genetic makeup a person had. Having a short version of the 5-HTT genetic code leads to a higher level of synaptic serotonine, which again leads to a higher level of amygdalar response to aversive stimuli. This is consistent with the prediction described above.

While these results have provided us new information about how genes regulate brain function, one can ask: does this have any effect on thought and behaviour? Indeed it has! Studies demonstrate that carriers of the s allele, compared to l allele carriers, are more likely to show abnormal levels of anxiety (5) develop affective illness (6) and even acquire conditioned fear responses (7). Variations in the genetic makeup of the serotonin system has profound influence on our experience and behavior. Thoughts are shaped by genes.

The original article contains several useful links. Check it out.

Not everyone wins the genetic lottery. At least now we are beginning to understand what happens, and what might be done to bring the advantages of good genes to the amygdalas of everyone.