Decoding The Engram

Decoding The Engram

By Vaishnavi Pernenkil

                Have you ever encountered a smell that reminded you of a person, or even a song that makes you reminisce about the past? It seems as if our memory encoding process is one that is unique to every individual, yet recent research by Dr.Chen at John’s Hopkins University states otherwise. Her recent fMRI study where participants were shown the first episode of the BBC show Sherlock and were told to retell their own versions of the same scene, showed that similar areas of the brain lit up when participants were recalling their experiences. This experiment paired with another one done by Sheena Josselyn from the Toronto Hospital for Sick Children try to decode the engram.

The engram, a term coined by the famous psychologist Karl Lashley is a physical trace of a single memory. Karl Lashley was the first psychologist to test lesioning studies in rats and tried to figure out the link between memory encoding and specific regions of the brain. His work focused on lesioning the cortex of rats and testing their ability to solve a maze. This study has now inspired new work regarding specific regions of the brain and memory encoding. A recent study done by Sheena Josselyn, “focused on boosting the memory protein CREB in some cells in the amygdala and showed that those neurons were especially likely to fire when mice learned, and later recalled, a fearful association between auditory tone and foot shocks” (Scientific American). They concluded that eliminating these CREB cells would then allow the animal to forget their fear. They tested this hypothesis by injecting a CREB protein toxin, and when reintroduced to this tone these rats did not show a fear response. This study shows that certain parts of the brain encode memories specifically and, “that there are specific rules by which cells become part of the engram” (Scientific American).

A separate study done by Dr.Chen at John’s Hopkins University tried to follow how memory recall occurs, and what specific regions of the brain are associated with memory recall. This study showed participants the first episode of the BBC show Sherlock and then studied brain activity when these participants recalled the episode. This study concluded that the hippocampus, and the posterior medial cortex lit up in all participants when recalling the first episode of the show, showing that recall patterns are very similar amongst multiple participants.  These studies are paving the way for understanding the engram and are getting close to decoding the engram. It seems as if the way we think are more similar than previously imagined. It is only with the advent of these fMRI studies and curiosity of brilliant minds that we are getting close to understanding how the brain remembers, and how memories are formed.

Works Cited

Shen, Helen. “Portrait of a Memory.” Scientific American, Scientific American, 14 Mar. 2018, www.scientificamerican.com/article/portrait-of-a-memory/.

The Modern Day Phineas Gage

Where would the field of neuroscience be without the extraordinary case of Phinease Gage? Gage was a railroad worker in the mid 1800's and at the time, his job was to drill holes and plant explosives to clear the way for a new railroad. After planting an explosive, he had to pack down the sand with what is known as a tamping iron. In a major accident, the explosive went off while tamping down the sand and the iron bar penetrated his left frontal lobe. After the accident, he survived, but had major changes in personality and his friends and family barely even recognized him anymore. He was studied by John Harlow. While this was the first time that a brain injury could almost certainly have been said to cause a change in personality, it sure was not the last.

Lisa Sanders of the New York Times wrote an article called Why Was Their Brother's Memory and Behavior So Strange? The article discusses a 49 year old man who, like Phineas Gage, experienced strange changes in his personality that progressively worsened. His family was dumbfounded as to why he was acting like a completely different person. In his 20's he had a problem with alcohol, but it was noted that even at the worst of times, he was still tidy and meticulous. Now he seemed to be very tired as he slept frequently and for long periods of time. He was also somewhat dirty and did not shower as much as he should have. The man had become very forgetful, was getting lost in familiar situations, and was let go from his job. Prior to his sister picking him up to go to brunch one day, he had called  her over 12 times to confirm the time and place. However, to her surprise, when she arrived to pick him up he was undressed and seem to have completely forgotten. What was his family to do? His sister decided enough is enough and took him to the emergency room.

The second doctor he saw noted that the man displayed no emotion, could not focus, had a very limited vocabulary, and could not even say what year or week it was. The doctor thought it could be dementia, but would be unlikely since the patient was so young. The man had a CT scan done and blood work which were both unrevealing. After taking an EEG, the brain appeared to be performing slower than usual. The next step was to get an MRI. The doctor got a call regarding the analysis of the MRI which indicated that the man had a rare condition known as severe spontaneous intracranial hypotension. The brain is normally surrounded by cerebral spinal fluid (CSF) which provides protection and helps the brain maintain its form. With his condition, the brain was lacking CSF and his brain was lying on the base of his skull. The cause was predicted to have been from a leak coming from a small hole in the dura which surrounds the brain and spinal cord. Eventually, with the help of a neurosurgeon from the West coast and an innovative procedure, the leak was able to be patched. The full recovery took four months and was strenuous. Today, the man is back at work and was able to enjoy seeing his family again.

References:

https://www.nytimes.com/2017/11/02/magazine/why-was-their-brothers-memory-and-behavior-so-strange.html

Circadian Rhythms and ADHD and Sleeplessness

After listening to Dr. Dan Cavanaugh's research on circadian rhythm, where he described an important relationship between sleep and circadian rhythms, which if aligned results in beautiful restful sleep. Sleep, Dr. Cavanaugh defined is when there is no conscious responsiveness of a person and very little physical movement throughout the duration of sleep. Dr. Cavanaugh interesting related sleep with coma but there is a vital difference, which is; during coma a person loses the ability to wake up due to some neurological damage whereas during a normal sleep a person is able to wake up to a strong external stimulus. Circadian rhythm have a huge impact on our body, it can be easily defined as our internal clock which tells the body when to fall asleep and when to wake up. Circadian rhythm develops constants sleep patterns and regulates the secretion of melatonin at a constant level to accommodate constant sleep patterns. However, if our sleep times are not constant and the pattern of our sleep is irregular, according to Dr. Cavanaugh this results in negative impact on our circadian rhythm which in turn is responsible for the regulating sleep. 

Reading an article on ScienceDaily.com about a connection between Attention Deficit and Hyperactivity Disorder (ADHD); according to Professor Sandra Kooij who presented her study at the ECNP Conference in Paris said that: "There is extensive research showing that people with ADHD also tend to exhibit sleep problems. What we are doing here is taking this association to the next logical step: pulling all the work together leads us to say that, based on existing evidence, it looks very much like ADHD and circadian problems are intertwined in the majority of patients." 

Interestingly, Professor Kooij said that 75% of ADHD patients experience sleeplessness.  Professor Kooij outlined that ADHD people often show greater alertness in the evening, which is the opposite of what is found in the general population. Finally, Professor Kooij stated what she will be looking into and asks a question "We are working to confirm this physical-mental relationship by finding biomarkers, such as Vitamin D levels, blood glucose, cortisol levels, 24 hour blood pressure, heart rate variability, and so on. If the connection is confirmed, it raises the intriguing question: does ADHD cause sleeplessness, or does sleeplessness cause ADHD?"

Both Dr. Cavanough and Professor Kooij highlighted that lack of sleep results in actual phenomenon called chronic sleep debt which can lead to many deleterious health problems. I find these two talk about circadian rhythm and sleep being disturbed by ADHD very interesting because considering these psychological sleep problems and abnormalities are a huge a problem for ADHD patients which one can think leads to many other long term diseases such as weight gain, diabetes, heart disease and cancer. 

Dr. Dan Cavanaugh 

Circadian Rhythms and Sleep in Drosophila Melanogaster 

Professor Sandra Kooij 

European College of Neuropsychopharmacology. "Is ADHD really a sleep problem?." ScienceDaily. ScienceDaily, 4 September 2017. <www.sciencedaily.com/releases/2017/09/170904093443.htm>.