The inner workings of the brain are extremely complex and not fully understood.
It turns out that memory is not just one function, but an array of operations with as many as 100 trillion synapses that create a network to help you remember something.
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Chemicals carry messages to cells forming links that reinforce memory. Retrieving that information takes another set of operations that use many parts of the brain.
Sometimes it seems like the answer is missing and then you remember sometime later. Or maybe something you always remember, like your phone number, is temporarily lost and it might take a few minutes to regain that information.
"Sometimes when you are trying to remember something, your brain may be slow in retrieving it because it is busy doing other things," said Dr. Sandra Weintraub, a neuropsychologist at the Cognitive Neurology and Alzheimer's Disease Center at Northwestern University's Feinberg School of Medicine. "However, the brain may continue to work even while you are not consciously aware of it. Then, the answer suddenly pops up at a time when you are doing something else."
Researchers are working on ways to help patients who have memory loss and Alzheimer's disease. Research shows the brain is always learning, revising and adjusting. When one part of the brain isn't working well, other parts of the brain might take on part of the lost function.
How do our brains perceive color?
The eye is designed to capture light, and certain cells within the eye help the brain to decode what it's seeing.
"There are nerve cells in the retina of the eye that are specialized for certain types of light information," Weintraub said. "Some cells, the rods, process the presence of light regardless of its color and others -- the cones -- are specialized for color vision."
Light is transmitted to the brain as chemical signals that make electrical impulses. The impulses travel to the brain through neuron extensions called axons.
"The information reaches the visual cortex where the signal is broken down into several different streams of information that are each then processed in a different part of that system," Weintraub said. "One part of the visual system processes lines and angles, another processes object movement and another processes color information."
Combine vision with memory and you get feelings -- like when you see a dog. If you've had bad experiences with dogs, seeing the dog might trigger a memory that makes you frightened. But good experiences might trigger a very happy feeling.