Unlearning Memories: You Have Been Erased!

In the movie 'Eraser', John Kruger, played by Arnold Schwarzenegger, removed the identities and all relevant information of persons-at-risk and gave them brand new identities, to save their lives. The title of this topic derives its name from the famous dialog: "You have been erased!”.

In reality, memories can be erased too, even long term ones! In humans, diseases like Alzheimer’s dementia, cause defects in short term memory limiting further memory acquisition; which finally progresses to erasure of previously stored memories. In experimental animals, long term memories can be prevented if they are subjected to electrical shock, anesthetics (possibly work by disrupting London forces operating in hydrophobic pockets in dendrites thereby causing 'unbinding' of memory elements), hypothermia and other insults within 5 minutes of learning a specific task.

There are guardians of memories keeping a constant vigil so that ‘memories are forever’. For example, we have seen masons at work standing on those makeshift scaffolds. In our bodies too, a protein called PKM zeta constantly ferries across the synapse, to give its healing touch. A protein called PSD-95, when phosphorylated, takes the role of the scaffold, in this analogy. Inhibitors of PKM zeta cause loss of memory, as demonstrated in rats, when their memories for tastes vanished after a single ‘shot’ in their taste cortex. So, LTP is not the only mechanism that fosters memory and neural plasticity. Long term memory also uses gene activation and expression, and protein synthesis. Any interruption in either of these mechanisms will have its own deleterious effect.

Genes have been identified which produce proteins that are necessary for memory formation and their maintenance. These genes act fast in the central nervous system and are known as IEGs (Immediate Early Genes). IEG Arc, one such gene codes for Arc protein, which is abundant in the hippocampal neurons. Obviously, the mRNA (messengerRNA can be thought of as ‘command’ from a gene, while proteins are like the results of this command) for that gene is formed in the nucleus by transcription, but once transcribed, it goes to the dendritic spines (especially those which are active) along the cytoskeletal rail road formed by microtubules. In the dendritic spines they (mRNA) translate themselves into proteins, Arc proteins, in this example.

Guzowski et al did an interesting experiment. They infused antisense oligodeoxynucleotide (for the inhibition of Arc protein synthesis) straight into the hippocampus of rats. Antisense oligodeoxynucleotides (antisense ODN) are short sequences of deoxynucleic acids which block the translation of mRNA into protein. The rats forgot the tasks they learned, while they could still form new memories. Their spatial memory was badly damaged. They concluded that antisense oligodeoxynucleotides interfered with the maintenance phase of LTP.

Rats can be challenged spatially using the Morris water maze. As we see in the picture, the water pool has two raised platforms, which rats can locate (and remember) spatially after some training. Even the rats already trained successfully, lost this spatial (co-ordinates in space) memory and had severe difficulty floating, when they were challenged with these chemicals. Looks like, You Have Been Erased!

Contradictory (against the motion) Link: Memories like diamonds may be forver

C. K. McIntyre (2005). Memory-influencing intra-basolateral amygdala drug infusions modulate expression of Arc protein in the hippocampus Proceedings of the National Academy of Sciences, 102 (30), 10718-10723 DOI: 10.1073/pnas.0504436102

The Organization of Memory And Internet Analogy

You are reading this particular article now on my website (in your computer and browser, of course!). There are billions of such websites and you picked mine. Perhaps you put your queries in the search box, which then showed you a list of results. You clicked my link there and lo, you are here!

The search engines (Google, Yahoo!, MSN and others) parse or read the webpages, index them and rank them. Each search engine has its own search robot, called bot, which crawls the pages. Now, this particular webpage that you are seeing is a part of my website. If you think of a website as a tall building, webpages may be considered as its floors. The search spiders not only crawl the website vertically (that is vertically up and down its individual floors), but they also move horizontally (clicking hyperlinks will lead you to arrive at some floor of another building) to be navigated to another webpage of another website.

Longitudinal (vertical) scanning picks up individual elements of the content, which are indexed (tagged) and remembered with respect to their locations, much like the human episodic memory in the hippocampus.

Now, its time for the bot to leave. It follows a hyperlink, if you have one, to a page of another website. So the search engine spider is directed to some floor in another building. Thus one might think of this search engine analogy to “neurodes and synapses” in artificial neural network. Here neurodes are the floors of the buildings and synapses are the hyperlinks (connections between them).

Next the search engine (Google) looks around in the floor to find similarities and dissimilarities from the floor it came. That is, it compares the webpages for relevance, in much the same way the anterior cingulated cortex (ACC) calculates “error related negativity” (ERN), and learns from it. It then calculates the ‘weight’ of association. It too learns from time to time by constant error related feedback, as happens in the ACC. Thus it assigns its hallowed “pagerank”.

PageRank is the relative importance of a page in Google’s eyes. ‘Page’ could come from Larry Page, co-founder of Google or more likely after ‘webpage’. One can see them in the Google toolbar in IE or Firefox, as a small green bar (Google’s own browser ‘chrome’ is yet to provide with a pagerank though). The lowest rank a page can have is 0, and the highest 10. Though the algorithm of pageranking is kept a secret like that of CocaCola, some insights may be had from “The Anatomy of a Large-Scale Hypertextual Web Search Engine” by Sergey Brin and Lawrence Page, founders of Google. I found a lot of resemblance of this paper with the architecture of learning and memory.


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Reference: hyper-links, unless specifically mentioned

Right is Might

You have forgotten your car keys and done hours of thinking; but to no avail. You give up in despair and start sipping your evening cup of coffee. Suddenly, out of nowhere you remember where you kept your keys. What you could not remember thinking, came so abruptly on its own. This is intuition and it is said that its the right brain (right half of the brain, obviously!) that is responsible for this. The famous scientist, Albert Einstein said “The only real valuable thing is intuition.”

When we copy a 'normal' picture, the 'logical' brain breaks down the picture into graphical pixels. These pixels are then plotted in their graphical co-ordinates. This is rather like mathematics. The picture on the left have been intentionally placed upside down. When you try to draw this picture, you just can not take anything for granted, because the orientation is just not right. The mathematical plotting can not be activated. Where reasoning ends, intuition begins. It is much easier to draw (copy a picture) a picture placed upside down, since our logic takes the back seat then; and the intuitive role of the right hemisphere ('intuitive brain') starts to play. We are no longer primed to 'assign' any coordinates preemptively. The right hemisphere of the brain is not only associated with intuition and drawing (art), but also emotion, music and other artistic abilities. The left brain is rather logical and deals with mathematics and other tasks that require calculations. When a subject is told to recall words, the activity in left frontal cortex increases (left parahippocampal area is also stimulated); while activities in the right frontal cortex (along with para hippocampal areas of both sides) are increased when a subject recalls sceneries or pictures. These activation patterns of the brain have been measured by fMRI scans (functional Magnetic Resonance Imaging), PET scans (Positron Emission Tomography), ERP studies (event related potential or evoked potential) and other medical investigations.

Have you noticed that when we hold babies in our arms, we put them on our left? This left cradling is puzzling, because its the right arm that is stronger. So, why do mothers hold their babies on their left laps? It has been suggested that our expressions show better on the left side of the face and left cradling fosters stronger mother-baby relationship. This arises from the fact that the hemispheres of the brain is cross-wired. The (some of the) neural pathways from the brain cross to the opposite sides, as they enter the spinal cord, to supply peripheral circuits. The right brain (the one responsible for emotion etc) is wired to the left side of the body and the left brain is wired to the right. Thus the 'emotion generator' right brain, will have its manifestation on the left side of the face. Mothers possibly don't bother about all this, but evolutionary anthropology has left its indelible footprints on bipeds.

To become a creative genius, you need both intelligence (a faculty usually attributed to the left brain) and intuition (typically a right brain's domain). Albert Einstein, it is said, had strong intuitive powers, which helped him to formulate his famous theory of relativity, ahead of the contemporary knowledge. So, its time we wake up to this fact and start exercising our right brains as well.