Why do we sleep? What is the purpose of sleep? Does something physiologically happen to our brains during sleep? Slowly, very slowly, scientists are providing us with some insights. The most complicated structure in all the universe.

The human brain and sleep, what do you know; T or F?

1. Neurons communicate through spaces called synapses.

2. Neurons are directly connected to each other.

3. During sleep all synapses remain large and strong.

All of us know the benefits of sleep. We are more mentally sharp, our moods are improved and we just plain feel better. We also know how awful we feel if we do not have enough sleep. We feel mentally foggy and are easily distracted. We are more irritable. We feel physically sluggish. The “why” of sleep is not well understood. However, neuroscientists are discovering some remarkable changes in the brain during sleep which may provide insights into the reasons and importance of sleep for brain function.

Neuroscientists at the Wisconsin Center for Sleep and Consciousness recently reported research findings using brains of mice which indicate that sleep plays a significant role in how nerve cells, neurons, communicate with each other. Nerve cells do not touch each other. Rather there is a space or junction, called synapse through which neurochemicals transmit information from one neuron to another — like notes being passed from one person to another. These neurotransmitters are critical to normal brain function. Some neurotoxins, for example, target synapses and neurotransmitters.

The neuroscientists found that during sleep there were changes in the sizes of some synapses. Some remained large and strong, indicating the importance of the information being transmitted at this junction. Other synapses shrunk, which may indicate the information at these junctions were relatively unimportant. The researchers postulate that this is a weeding out of unnecessary signals which just clutter the brain and get in the way of streamlined communication between more important neurons. They think that this is one reason sleep is so critical to normal brain function. Sort of like cleaning up the kitchen before you retire for the night so in the morning you can start fresh and new. The scientists describe this as a “resetting.”

To conduct this four-year study, very expensive, sophisticated imaging was used to view microscopic changes at the synapses. During the day, when the brain was stimulated with new experiences and information, the synaptic spaces enlarged. During sleep, synaptic junctions shrank. The scientists refer to this as “synaptic homeostasis hypothesis” or SHY. In SHY theory it is thought that daytime stimulation results in synapses becoming larger and stronger in response to learning and memory. During sleep, when there is very limited external stimulation, the brain is able to weed out or shrink synapses that are not particularly important. This provides for enhanced learning, through reinforcement of neurotransmission at certain junctions, at the same time the brain declutters. Our Master Gardener friends may compare this to pruning some flowers to bolster the growth of others.

This reminds me of something I was told many years ago, “If everything is important, nothing is important.” It appears sleep may be a governor which helps prioritize or reinforce important memory and learning and rids us of that which is relatively unimportant. Might this partly explain why academic performance and recall on tests is higher among students with good sleep habits? Time will tell. Research like this provides us with direction for future study and improved understanding of not only how we lay down memory and learning but the role of sleep in this process. How’s your sleep?

Answers: 1. T; 2. F; 3. F


-- Dr. Lori Boyajian-O’Neill, DO, can be contacted at lori.boyajian-oneill@hcahealthcare.com.