That late night fridge raid may seem harmless but making it a habit may affect learning and memory, a new study suggests. Eating at times normally intended for sleep causes a deficiency in processes controlled by the hippocampal portion of the brain.

Researchers from the University of California, Los Angeles, found that circadian rhythm is important for health and cognitive function. With the fast-paced life most people lead nowadays, their circadian system is affected by inappropriate meal or work times. The researchers scheduled food access in relation with sleep time to see how the factors affect learning and memory.

In the study published in the journal eLife, the researchers conducted experiments on laboratory mice. A group of mice were fed earlier than the time intended normally for dinner while those in the other group were fed late at night - right before sleeping time.

These mice were given a mild shock and the next day, they were placed in the same spot. Those who ate early felt scared, which means they remembered the shock. The other group who ate late at night did not manifest fear response, showing how their memory was affected.

The researchers say that this is because the mice who ate when they should be sleeping had lesser levels of a protein called CREB (cAMP response element-binding protein), which is the key for the body's internal molecular clock and the brain's capability to form memories.

"We have provided the first evidence that taking regular meals at the wrong time of day has far-reaching effects for learning and memory," study author Dawn Loh said.

Loh added that eating at times the brain should be resting may "dull some functions of the brain".

"Since many people find themselves working or playing during times when they'd normally be asleep, it is important to know that this could dull some of the functions of the brain," she added.

The study shows that learned behaviors are more affected in the experiment. The mice who were regularly fed at times they should be sleeping were less likely to recall the object. Long-term memory was also altered.

Long-term memory and the ability to recognize a novel object are controlled by the hippocampus. The study sheds light on past information about the effects of circadian rhythm alterations to the body specifically to the brain.

"In this study, we sought to determine if temporally restricted feeding schedules in mice could impact cognition. We found that time-restricted feeding led to dramatic impairments in learned behaviors such as hippocampal-dependent contextual fear conditioning and novel object recognition," the researchers wrote in their study.

"The reduction in tCREB (total CREB) provides a biochemical explanation for our finding, as well as providing a guidepost for future analysis of the effects of the misaligned feeding in the hippocampus. Therefore, this work raises the possibility that the timing of when we eat alters the physiological and biochemical events underlying learning and memory," they added.

What is the role of the hippocampus?

The hippocampus is the region of the brain that governs learning, memory and emotions. Specifically, the hippocampus is involved in the storage of long-term memory which involves all past knowledge and experiences.

Aside from memory, the hippocampus is also responsible for special navigation. In diseases like Alzheimer's disease, the hippocampus is one of the parts of the brain that is altered and damaged, leading to memory loss and disorientation.

This region of the brain is also sensitive to lack of oxygen. It can be damaged through hypoxia or lack of oxygen in the brain, infection or inflammation. Mostly, people who have a damaged hippocampus develop amnesia or the inability to recall past memories. In some cases, people may be unable to form new memories of the time or location of an event.

Understanding the circadian clock or rhythm

The circadian clock is controlled by the Suprachiasmatic Nucleus (SCN). Found in the hypothalamus, these cells respond to light and dark signals. When the optic nerve in the eye senses light, it travels to the SCN which signals the internal molecular clock that it is time to be awake. At night, melatonin, a hormone which is associated with sleep onset increases, promoting sleep.

Photo: Pete Markham | Flickr

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