Memories are not located in one particular place in the brain. They are a brain-wide process. Encoding is the first step in creating a memory. Sensations like physical features of an individual or, colour, scent or smell of a fruit, travel to the hippocampus in the brain, separately. The hippocampus integrates these perceptions into one single experience of a specific person or a fruit. The hippocampus, along with the frontal cortex, another part of the brain, then analyses these various sensory inputs and decides whether they are worth remembering. If they are, they become part of our long-term memory. Various bits of these information are then stored in different parts of the brain.
Although memory begins with perception, it is encoded and stored using the language of electricity and chemicals. The electrical firing across the synapses triggers the release of chemicals called neurotransmitters. These chemicals diffuse and reach the neighbouring cells. As we learn and experience the world, changes occur at the synapses. More connections are created in the brain. It organises and recognises itself in response to our experiences, forming memories, triggered by the inputs prompted by experience, education or training. These changes are reinforced with use and practice.
Synapses or connections between nerve cells (neurons) are responsible for transmitting nerve signals. Making, breaking, strengthening or weakening of synapses will directly affect learning and memory.
The brain encodes huge amounts of information, but only a small fraction is stored for a longer time. There is now compelling evidence that the long-term storage of memories preferentially occurs during sleep (Journal of Neuroscience, 2011). Sleep plays an important role in memory, both before and after learning a new task. Lack of adequate sleep affects mood, motivation, judgment and our perception of events. Good sleep through the night is optimal for learning and memory. However, the factors involved in sleep-associated memory consolidation are poorly understood.
Erasing memories is as much of interest to researchers as its consolidation. A new study (Nature, January 2010) has shown that updating memories of fear with non-fearful information provided through extinction training blocks previously learnt fear responses and leads to a lasting change in the original fear memory. These results have significant implications for the treatment of anxiety disorders.
Current form of therapy relies on extinction, but it has the drawback that extinguished fear could resurface under certain conditions. The discovery that certain pharmacological agents can erase memory was encouraging. However, most of these compounds were found to be toxic to humans. The current study proposes a more natural intervention, allowing a safe and easily implemented way to prevent the return of fear. This is based on the premise that re-consolidation is an adaptive update mechanism by which new information is incorporated into old memories. By introducing new information during the re-consolidation period, it may be possible to permanently change the fear memory.
Old age and
As we grow older, memory problems tend to increase. Older people may experience decreased blood flow to the brain which could impair memory. The production of growth factors—hormones and proteins that protect and repair brain cells and stimulate neuronal growth—also declines with age. The synapses also begin to falter, which begins to affect the ability to retrieve memories.
One of the reasons for the deterioration of memory could be the major cell loss in a tiny region in the front of the brain. These cells are responsible for the production of a neurotransmitter called acetylcholine, which is vital to learning and memory. Another important area, hippocampus, loses 5 per cent of its nerve cells with each passing decade for a total loss of 20 per cent by the time we reach age 80. The memory decline can also be due to several other factors like unhealthy gene inheritance, exposure to poisonous substances, smoking and excessive alcohol consumption.
loss vs dementia
The primary difference between age-related memory loss and dementia is that the former is not disabling. The memory lapses have little effect on our ability to undertake day-to-day tasks. Sometimes, even what looks like significant memory loss can be caused by treatable conditions and reversible external factors. They could be side effects of medications such as antihistamines, blood pressure and arthritis medication, antidepressants and painkillers.
Depression can mimic the signs of memory loss. Vitamin B12 deficiency that protects neurons can sometimes cause permanent damage to memory. Older people have a slower nutrition absorption rate, which makes it difficult for them to absorb the required amount of vitamin B12. If the vitamin B12 deficiency is addressed in time, the associated memory problems can be reversed.
The brain is capable of producing brain cells at any age, so significant memory loss is not an inevitable result of ageing. Our lifestyle, health habits and daily activities also have a huge impact on the health of our brain.
Dr Kumar is director of Microscopy Imaging Core Facility at the Center for Dementia Research, Nathan Kline Institute for Psychiatric Research; assistant professor, Langone New York University School of Medicine, and research scientist at the Center of Excellence in Brain Aging and Dementia and Neuroscience Center, New York.
The power of plasticity
The human brain has an amazing capability to adapt and change, even in old age. This ability is known as plasticity. With the right kind of stimulation, our brain can form new neuronal pathways and change existing interconnections. We can use our inherent power of neuroplasticity to increase our cognitive abilities, to enhance our ability to learn new information and to improve our memory.
Get moving Our ability to remember will improve when we provide our brain with a good diet and practice other healthy habits. Adequate blood circulation is very important for the health of the brain. Blood carries oxygen and nutrients for the well being of neurons. Physical exercise increases oxygen supply to our brain and reduces the risk of other disorders that lead to memory loss such as diabetes and cardiovascular illness. It also enhances the effects of helpful brain chemicals and protects the brain cells. New research shows that walking six to nine miles every week can prevent brain shrinkage and memory loss. According to American Academy of Neurology, older adults who walked between 6 and 9 miles per week had more grey matter nine years after the start of the study as compared to those who did not walk.
Sleep well When we are sleep-deprived our brain cannot function at full capacity. Creativity, problem-solving abilities and critical-thinking skills are hampered. Sleep is critical to learning and memory.
Be socially active Several studies have shown that a life with friends and fun activities provide cognitive benefits. Healthy relationships stimulate our brain cells and interacting with others may be the best kind of brain exercise. It has been reported that people with the most active social lives had the slowest rate of memory decline. Laughter engages multiple regions of the brain and laughter is, indeed, the best medicine. Listening to jokes activates areas of the brain vital to learning and creativity. Spending time with children is also good for the brain.
Meditate Studies have shown that meditation alleviates conditions such as depression, anxiety, chronic pain, diabetes and high blood pressure. Meditation can also improve focus, concentration, creativity and learning and reasoning skills. It is believed to increase the thickness of the cerebral cortex and encourage more connections between nerve cells—all of which increases mental sharpness and memory ability.
Eat right The brain needs a lot of fuel to function well. A diet based on fruits, vegetables, whole grains and healthy fats is good for memory. More and more evidence indicates that Omega-3 fatty acids are beneficial for brain health. Sources of Omega-3 fatty acid include walnuts, ground flaxseed, flaxseed oil, pumpkin seeds and soya beans. It is advisable to avoid red meat, whole milk, butter, cheese, sour cream and ice cream. It is important to have lots of leafy vegetables such as spinach, broccoli, lettuce and fruits like apricots, mangoes and watermelon. Drink wine or grape juice in moderation.
Carbohydrates are fuel for our brain, but simple carbohydrates like sugar, white bread and refined grains give a quick boost followed by a rapid crash. Complex carbohydrates such as whole-wheat bread, brown rice, oatmeal, high-fibre cereal, lentils and whole beans provide energy that lasts longer.
Keep the brain busy The more we work out our brain, the better will it be able to process and remember information. Brain activity needs to be something that is out of our comfort zone, like, for instance, learning a new language, an instrument or sport, or tackling a very challenging crossword puzzle. The activity should be exigent, but not so difficult that we end up not doing it. Playing games that involve strategy, like chess and bridge, and reading magazines and books that challenge our existing knowledge are good for keeping the brain busy.
Stay hydrated Dehydration is a common problem in older people and severe dehydration leads to confusion, drowsiness, memory loss. It is important to stay hydrated. Drink six to eight glasses of water a day.
Pay attention It takes not more than 8 to 10 seconds of intense focus to assimilate a piece of information into our memory. If you are distracted, find a quiet place where there is no disturbance.
Involve as many senses as possible The physical act of rewriting information might help register it in our brain. Even if we are good at visual perception, reading out loud what you want to remember is very helpful. Some people try to recite rhythmically and that helps. Also, try to connect new information to that you already know.
Think basic and repeat At the time of learning complex material, focus on understanding basic ideas rather than memorising isolated details. Explain the newly learned complex information to someone else in your own words.