Archive | Learning and Memory

Memory is ‘team effort’

Posted on 05 August 2011 by Dr Paul

Check out this article on the BBC website about the work conducted by many of my coworkers and friends at the University of Bristol.

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‘Terry Pratchett: Choosing to Die’ series part 1: Alzheimer’s disease

Posted on 15 June 2011 by Dr Paul

What is Alzheimer’s disease?

Terry Pratchett is probably the most well-known person to have a particular form of dementia known as Alzheimer’s disease and in his recent documentary he revealed that having the disease is making him contemplate assisted suicide. But what is Alzheimer’s disease and why haven’t neuroscientists cured it yet?

Alzheimer’s disease is a neurodegenerative disease, which means that neurones (brain cells) in the brains of sufferers begin to degenerate and, as a consequence, regions of the brain (such as the hippocampus and parts of the cerebral cortex) shrink severely as the disease progresses.

Common symptoms include loss of memories, loss of the ability to form new memories and loss of the ability to perform complex motor functions. All of these symptoms worsen with time and eventually lead to an inability to perform even the simplest function and then death.

What are neuroscientists doing to help?

Alzheimer’s disease is probably the most studied illness of the brain and represents one of the major challenges for neuroscientists of our time. But given the intensity of the research in this area, surprisingly little is actually known regarding what causes the disease.

However, there are two main theories (which are not mutually exclusive) about what may be the cause. These involve a protein, a peptide and lot of tangling.

First, a word on proteins. For people not involved in the biological sciences, the word ‘protein’ may conjure up images of bodybuilders or the information found on the back of food packets. But proteins are responsible for a lot more than building body mass. They are the building blocks of life, and the complex interplay of the different proteins that exist in your body govern how you think, feel and respond.

Proteins serve many purposes in the human body and can take many forms. However, they are all made out of the same little units (amino acids), which can be arranged in a multitude of different ways.

One of these proteins, known as tau, helps to stabilise microtubules (part of the cell skeleton that determines the shape of the cell and assists the transport of molecules within it.) In Alzheimer’s disease, this protein attaches itself to other tau proteins inside the cell to cause a tangled mess of proteins, known as neurofibrillary tangles. This may be one of the causes of the neurodegeneration that occurs during Alzheimer’s.

Now, a peptide is just a smaller version of a protein, and a peptide known as amyloid beta may also be one of the contributors to the onset of Alzheimer’s disease for a very similar reason. Different forms of amyloid beta can attach to each other to form complexes known as ‘plaques’ and these plaques are observed in the brains of patients who have died from Alzheimer’s disease. Furthermore, some forms of amyloid beta may actually be toxic by themselves.

So, at present, neuroscientists believe that these protein tangles and peptide plaques may hold the answer to why neurones begin to degenerate following the onset of Alzheimer’s disease, but has this helped with its diagnosis or treatment?

How do you know someone has Alzheimer’s disease?

The short answer to this question is: you don’t. Well, not for certain at least.

At present, psychological assessments can be made that can distinguish patients with Alzheimer’s disease from patients without dementia with a high degree of accuracy, but these fail to accurately detect differences between patients with other forms of dementia and Alzheimer’s.

Brain scans such as CT (computerised tomography) and MRI (magnetic resonance imaging) can be used in conjunction with psychological assessments to rule out other pathologies that might be causing the observed symptoms, such as tumours.

But the real problem is that the symptoms of Alzheimer’s disease are so similar to a range of other illnesses that lead to dementia, diagnosis is extremely difficult.

However, because of the work achieved within neuroscience research, techniques that measure the amount of amyloid beta and tau protein present in the circulation of patients are now being employed in order to assess possible Alzheimer’s sufferers.

In reality, a range of different techniques involving those mentioned as well as other complimentary procedures will need to be utilised to unequivocally diagnose a patient with Alzheimer’s disease. But once a patient has been diagnosed, what can be done to treat them?

What can be done to treat Alzheimer’s disease sufferers?

Unfortunately, at this point in time, relatively little.

There are some treatments available that do improve cognitive function once it has declined, such as memantine and cholinesterase inhibitors. Also, improved social interaction and aromatherapy offer non-pharmacological alternatives to the aforementioned treatments. However, these treatments appear to have only limited effects and do not cure the disease.

For obvious reasons, attempts to find a cure for Alzheimer’s disease have centred around the prevention of amyloid beta plaque and neurofibrillary tangle formation.

Unfortunately, immunotherapy techniques (which utilise antibodies) that have cleared amyloid beta fragments from Alzheimer’s patients have been ineffectual in curing the disease. In fact, no treatment that has targeted amyloid beta has been effective. This has sparked debate as to the role of amyloid plaques in causing the disease.

It isn’t all bad news though. Some promising results have begun to emerge from treatments designed to disrupt the formation of neurofibrillary tangles and these may turn out to be the treatments of the future, once they pass through the necessary medical trials.

Can I stop myself getting Alzheimer’s disease?

Well, no one knows exactly how to prevent Alzheimer’s, but there are several risk factors that are associated with the development of the disease.

There are a couple of things that you are powerless to stop that increase your chances of getting Alzheimer’s disease, such as age, genetic make-up and if you sustain a head injury. There are also treatable conditions that are associated with an increased risk of developing the disease, such as stroke and diabetes.

But there are also several things you can change as a matter of lifestyle that can lower your chances of developing Alzheimer’s. These include (yes, you guessed it) decreasing alcohol consumption, having a healthy, balanced diet, increasing the amount you exercise and giving up smoking. Also, there are some reports that an increase in social activity and having a mediterranean diet may reduce your chances too.

Alzheimer’s disease is a complex condition. It is hard to diagnose, to treat and to work out what is causing it. Progress will take time, but there is hope on the horizon. Neuroscientists are working tirelessly to find a cure (and secure a nobel prize) and they have already made important steps in determining the cause of the pathology.

While they are working on it, the best advice I can give for preventing Alzheimer’s is: Stop drinking and smoking and eat more fresh fish and pasta!

In all seriousness, Alzheimer’s disease causes turmoil for those who suffer from it and those who care for them. Patients are often aggressive and can become depressed. This, coupled with the fact that they often lose all recollection of the identity of their loved ones, makes caring for a patient with Alzheimer’s an extremely stressful experience. I sincerely hope that a cure can be found soon.

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Fruit fly may hold key to visual memory

Posted on 10 June 2011 by Dr Paul

Flies are a pain in the neck. Let’s be honest, when the room is invaded by a big, buzzing intruder, the majority of us reach for the rolled-up newspaper. But few will realise that one of these aerial invaders has been at the centre of neuroscience research for many years. Because flies have a less complex nervous system than their mammalian counterparts, the common fruit fly(Drosophila melanogaster) has served as a useful model for studying the neural networks involved in behaviours that are observed in both humans and fruit flies (such as sensory perception and learning and memory.)

In a recently published study, researchers from the Howard Hughes Medical Institute have used innovative techniques to demonstrate that the common fruit fly uses its vision to learn how to navigate (known as ‘visual place learning’). Ashumans use the same process whilst navigating, understanding how organisms with less complex nervous systems achieve this form of learning may shed some light onto how humans do it also.

Researchers placed fruit flies in a small arena with walls that were under temperature control. All but one panel of the arena were kept at a temperature that was higher than would be comfortable for a fly to rest on. This meant that flies gradually made there way to the ‘cool’ panel after entering the arena. Surrounding the arena walls were visual cues such as crossed lines and parallel lines that the fly could use in order to orientate itself within its environment. After an initial phase, where flies entered the arena and made their way to the platform for the first time, flies were then taken out and then put back in and the time taken to find the ‘cool’ platform was measured.

As the test phases progressed, flies got quicker at finding the ‘cool’ platform, which demonstrated that they had learnt where the platform was. Interestingly, when the platform and the visual cues were moved such that they were in the same relative position, flies still made their way to the ‘cool’ platform quicker than when they were first introduced into the arena. However, if the visual cues were not moved (and the platform was) or the flies were put into the arena in the dark, they failed to show any improvement in finding the ‘cool’ platform, suggesting that the flies were using their vision to learn the position of the platform.

Now, mammals are well known to be able to locate themselves in their surroundings using visual cues. In rodents, an area of the brain known as the hippocampus contains separate regions that encode different aspects of the spatial information. This is a fairly complex structure consisting of several integrated layers. What is fascinating about the current finding is that fruit flies have the ability to locate themselves in exactly the same manner, but do it with a much simpler nervous system. In fact, by actually repressing the ability of certain cells to work, the researchers were able to demonstrate that a small subregion of a part of the fly brain known as the central complex ellipsoid was all that was necessary for visual space learning.

This study has shown that the common fruit fly is a valuable tool in understanding visual learning and that further research using these winged beasts may reveal the systems that underly this process across a variety of different lifeforms. Perhaps the mammalian system is just a more complex version of the fruit fly system or maybe these two creatures have developed distinct solutions to a shared problem. It is likely that there is some truth in both of these propositions, but one thing is for certain, you should think twice before you next grab that newspaper, that fly knows how to find you!

See: Visual place learning in Drosophila melanogaster (Ofstad et al., 2011. Nature)


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