An article recently published in Medical Xpress outlined research into memory recall in Rett syndrome patients. Not only did it look into the underlying causes of diminished memory recall, but it found a method that could possibly improve it as well. You can find the full study here, where it was published in Neuron.
About Rett Syndrome
Firstly, it’s necessary to understand what this rare disorder is. Rett syndrome is a severe, rare neurological disorder that primarily affects females. It was once thought to be a form of autism but has since been distinguished as its own condition. It is a genetic disorder, with a mutation occurring on the X chromosome. The exact location of this mutation and its effects are unknown, but researchers do know that it is typically a sporadic mutation. Symptoms of this condition usually appear between the first 12-18 months of life. Effects include slowed brain growth, a small head, issues with muscle coordination, social anxiety, lack of language skills, seizures, uncoordinated breathing, and a tense or irritable disposition.
After these symptoms are noticed, doctors will conduct a clinical examination and rule out other conditions, such as autism. Genetic testing will be used to confirm, and it can also show the severity of a specific case. There is no cure for Rett syndrome, and treatment consists of symptom management. Doctors will suggest physical, speech, and occupational therapy. They may also prescribe anti-seizure medications.
About the Study
Led by Dr. Huda Zoghbi, this study investigated long-term memory recall in those living with Rett syndrome. The investigators already knew that contextual memories are diminished in affected individuals, and that hippocampal neurons play a role. Specifically, the excitatory/inhibitory synaptic inputs were being looked at in the prior research that influenced this study.
Armed with this knowledge, Zoghbi and his team crafted their hypothesis, which stated that disruptions in the balance between these synaptic inputs may alter hippocampal neurons. As these neurons are needed for contextual memories, the disruptions consequently alter memory recall as well.
In order to investigate their hypothesis, the researchers monitored mice models of Rett syndrome as they recalled a scary memory using a miniature microscope. Their observations told them that there was a lack of inhibition to the hippocampal pyramidal neurons. While this was a very helpful step in research, it also unlocked more questions. Specifically, the team wondered which neuron is at fault for this lack?
This next step in the study saw Dr. Zoghbi and team record neuronal activity in brain slices with identified cell types. They discovered a reduced connection between a form of somatostatin-expressing (SOM) inhibitory neurons and pyramidal cells. Further analysis revealed that these neurons were poorly engaged in the models of Rett syndrome. So the question arises: would engaging these neurons improve memory recall?
After selectively enhancing these cells through a chemical-genetic approach, the researchers saw that memory recall was restored. While further research is needed to understand this process in humans, this is a very large step in the right direction for combatting memory impairments in Rett syndrome.
