Oxytocin is a very powerful hormone. This neurotransmitter is important in many social, parental, and stress-related behaviors, and its high levels during sex, childbirth, maternal care, social recognition, and pair bonding has given it the status of being the “love hormone.” New research and previously published studies all demonstrate the link between oxytocin and autism.
Autism and Oxytocin: Studies
Autism spectrum disorders are often connected with deficiencies in oxytocin levels and mutations in the oxytocin receptors.
- In a 1998 study, for example, autistic children showed significantly lower levels of oxytocin than normal.
- Another study, in 2003, found that the intravenous administration of oxytocin reduced some repetitive behaviors.
- In addition, a study in 2007 showed that oxytocin helped autistic adults “evaluate the emotional significance of speech intonation.”
Researchers have found that oxytocin increased the firing of inhibitory neurons; not how elevated inhibition could help with information processing in the brain.
In a new study, Owen et al. “described a simple yet powerful mechanism by which oxytocin enhances cortical information transfer while simultaneously lowering background activity” and showed how “a diffusely delivered neuromodulator can improve the performance of neural circuitry.”
Electrophysiology to Measure Response
Owen et al. used electrophysiology to measure electrical activity of neurons in a part of the hippocampus (CA1). They used electrodes to stimulate the Schaffer Collaterals, activating both excitatory pyramidal cells and inhibitory cells.
Neurons are often described as ‘noisy,’ usually firing without external stimuli. Because of this, finding the right information can be difficult; the signal of interest needs to be strong and the background noise needs to be weak.
In order to see how oxytocin works, Owen et al. stimulated axons leading to the CA1 area of the hippocampus to create artificial information. When they used an oxytocin-like molecule (TGOT) to stimulate oxytocin receptors, the excitatory neurons were much better at transferring the signal to the next neuron. This increases the fidelity – giving other receivers a better change as getting the information. When compared to baseline measurements, the excitatory neurons’ activity decreased.
Researchers used different chemical blockers and electrophysiology to find a type of inhibitory neurons, fast-spiking interneurons (FSI), that are more abundant and stronger in spontaneous firing. This creates an overall inhibitory setting that decreases background noise.
Autism Treatment: Significance of this Study
According to Dr. Richard Tsien, professor and chair of the Department of Neuroscience and Physiology and director of the Neuroscience Institute at NYU Langone Medical Center, there is only one population of FSI that is activated by oxytocin. When this happens, the FSIs’ firing rates increase, resulting in a decrease in background noise and an increase in signal. Dr. Tsien tells Decoded Science: “It’s the fact that activating one cell type can do both of these things that makes our finding exciting.”
The decrease in noise happens because the rate of firing of FSI goes up, causing more inhibition, and therefore reduces spontaneous noise. The increase in signaling is a bit harder to see.The “hippocampal circuit uses fast spiking interneuron right along with excitation,” in a feedforward inhibition action.
Dr. Tsien describes it “like a car driver using both of her feet, one on the accelerator and the other on the brake, one right after the other, to allow the car to lurch forward by the right amount. In much the same way, the hippocampal circuit excites, then inhibits in quick succession, using the braking effect to cut short the accelerator action, and thus achieve precision timing.”
Oxytocin causes inhibitory neurons to fire, causing the connections to wear down. This is like “tiring out the braking foot from continual use on a long downhill road.” So when a signal arrives at the circuit, it is more to be passed and causes an action. Because of this information can be passed through in a more reliable manner.
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