Consolidation and Reconsolidation with Memories

The brain controls the body both physically and emotionally. Thousands of neurons work cooperatively to send signals and to express emotional statue. The human brain became an ambiguous puzzle to scientists that it led to significant in-depth research in the form of experimenting with patients and performing surveys that the scientists could then use to conclude the results around the function of the human brain. It is still an enigma, in which scientists are still trying to master the piece. However, out of all those human brain functions, memory became key factor to the research community and to individuals because of its ability to identify their daily habitat. Memory consolidation is the mechanism of how the brain processes and stabilizes memory after its initial acquisition. Memory consolidation can be divided into three different phases. The first phase is synaptic consolidation where chemical signals and electric pulses pass through hundreds of synapses that are represented as networks of the brain. When neuroscientists talk about synaptic consolidation, they relate it to long-term memory process. The second phase is system consolidation where electrical and chemical signals reach hippocampus and memories are processed. Lastly, the third phase, which is reconsolidation is the focus of Kathleen McGowan’s article How Much of Your Memory Is True? and Ed Yong’s article Rewriting Fearful Memories by Bringing Them Back to Mind. 

Reconsolidation is a process where memories that were formed from previous events can be displaced or altered through external stimuli. The article opens with Rita Magil’s car accident story. Magil was in a car accident and during the car accident; the cement pillar from the building tore through her car and stopped only about a foot from her face. After this accident, it gave Magil post-traumatic stress disorder (PTSD), which caused her to think about the memory of the cement barriers emerging towards her. This disorder gave her uncomfortable symptoms such as a rising heart rate, sweating and feeling jumpy. McGowan claims that people who survive from accidents and attacks never end up developing PTSD. However, Magil’s case was odd and thus neuroscientists performed experiments to treat her disorder. The scientists used propranolol that decreases the activity of amygdala where emotions are processed from the brain. As a result, propranolol blocked the action of adrenaline, and caused the neuroscientists to treat Magil’s PTSD. The drug treated the anxiety associated with the past memory, but her memory of the incident was still there. Therefore she did not get rid of the memory entirely but was able to edit it. In other words, she was able to restructure her memory of the accident, separating fear and the facts. The event from Magil caused other neuroscientists to perform further experiments to understand how memory works in our brain. Throughout these experiments, they found that memory can be rewired or changed in the brain, and possibly make the associations with these memories disappear. These findings provide neuroscientists with hope that they can help cure PTSD and other mental illnesses.

When we compare technology from the past, we realize how much the technology that we use to help us solve problem has significantly improved. Neuroscientists, who study the function of the brain, thought of memory as a “kind of neural architecture, a literal physical reshaping of the microstructure of the brain”. However, neuroscientist Santiago Ramón y Cajal proves other scientists wrong by discovering how the different structure of synapses can cause a change to memories. Further investigation of how memories can be changed was stimulated to other neuroscientists after Cajal’s discovery. According to the article, the author claims that most neuroscientists believe that the active function of glutamate and electrical pulses cause memory to be formed in the amygdala and hippocampus, which are the subunit of the brain. When someone receives information and tries to memorize it, the information in their brain is not concrete enough to have solid memory in their brain until the memory ‘solidifies’ or stays in one’s brain for long time. The author explained this particular process by claiming that memory is “consolidated”.

Although changing the structure of synapses and using chemical drugs can change memories, some neuroscientists proved that false information could be implanted to the human brain. Moreover, other scientists who are investigating the concept of memories in our brain found that false memory is a normal phenomenon. The term reconsolidation is defined as a memory that is reactivated and destabilized, exposing it into a flexible, vulnerable state, which insists that a memory can be altered or changed. Nader conducted an experiment to test a reconsolidation process. The experiment suggested that it was indeed reactivation that made this consolidated memory instable again. An interpretation of the experiment implied that the reactivation of a consolidated memory changes it to enter a labile state from which it has to re-stabilize or reconsolidate over time. This proposed that memories are not consolidated or stabilized just once; they can be reactivated, become vulnerable, and be stabilized. Therefore, consolidation and reconsolidation begin with a transient period of instability. In the case of consolidation, this phase is initiated after acquisition of new information. In the case of reconsolidation, it is initiated after the reactive of an existing, consolidated memory. Only during the reconsolidation phase can memory be enhanced, impaired by amnesic treatments or interfered with by new learning. More research of reconsolidation promoted more findings. Reconsolidation research supported that the flexibility of memory might be functional; it is like how we update our knowledge by making old memories susceptible to new facts.

As mentioned above, reconsolidation is a somewhat controversial term. I agree with Nader’s proposal that a consolidated memory can be reactivated and reconsolidated. However, reconsolidation still needs to be studied further to provide an applicable and reliable protocol. I believe that memories are plastic and flexible all the time. For a specific time, they can be more pliable, but memory has to be always flexible in order for us to successfully remember. However, memory being flexible can be problematic as well. As previously mentioned, every time a memory is reactivated and reconsolidated, memory can be altered and changed. “Nader’s group discovered that the NMDA glutamate receptors were involved in destabilizing the memory”. The more reactivation a memory goes through, the more vulnerable it becomes to a change. The experiment conducted by Nader supports this proposal. The experiment concludes that reactivation is needed for a memory to become labile and to be re-stabilized again. His hypothesis and his experiments have shown to match.

The second article called “Implications of Memory Modulation for Post- Traumatic Stress and Fear Disorders” is published by Ryan G Parsons and Kerry J Ressler. Post-traumatic stress disorder, panic disorder and phobia display an uncontrollable state of fear. Their development involves heredity, previous sensitizing experiences, association of aversive events with previous neutral stimuli, and inability to inhibit or extinguish fear after it is chronic and disabling. The consolidation of fear conditioning refers to the alteration of memory from a labile state immediately after acquisition to a more permanent state. Treatments that disrupt the consolidation of memory are usually applied a few minutes to a few hours after conditioned-unconditioned pairings. The treatments leave short-term memory intact but interfere with formation of long-term memory. This implies that exposure to appropriate therapy after trauma may lead to more rapid recovery or even prevention of PTSD formation. The observation that fear memories can be disrupted by combining retrieval of memory with drug treatment opens up the possibility of using this strategy to treat fear related disorders.

Studies of reconsolidation indicate that there may be limitations to using a reconsolidation-disruption approach as a way to treat fear-related disorders. Retrieval does not always trigger reconsolidation. Older and stronger memories are less susceptible to disruption after retrieval. Traumatic memories are usually stronger. Once again, the concept of reconsolidation is somewhat controversial. Reconsolidation needs more research to be universally validated. However, if reconsolidation can be further developed, it may be used to treat patients with PTSD. However, in order to do so, reconsolidation has to successfully overcome all the negatives mentioned in the previous paragraph. The last article “Engineering a memory with LTD and LTP” written by Sadegh Nabavi and his colleague mainly focus on long term potentiation (LTP) and long term depression synaptic (LTD) and how those long term functions process synapses and memory. Nabavi and his colleague performed experiments with conditioned animals by shocking their food with optogenetic stimulation of auditory inputs mainly focusing on amygdala. By performing this experiment, the scientists inactivated and reactivated memory using LTD and LTP.

The scientists measured the AMPA receptor component and NMDA receptor component from synaptic response by examining prepared amygdala brain slices from the animal. Out of this experiment, their purpose was to figure out if the memory can be inactivated. The author claims that memory is inactivated when memory contribution long-term potentiation (LTP) occurs at synaptic onto the lateral amygdala. Moreover, animals were tested with optical CS and showed no CR, which proves the inactivation of the memory that was shocked with long term depression (LTD). Additional experiments that were performed were to examine if there is an opportunity for memories to be reactivated by following an optical LTP protocol. After one day, animals showed a conditioned response (CR), which shows the reactivation of the memory. These results prove that synapses are able to perform multiple times of bidirectional plasticity. However, performing second optical LTD protocol, the animals did not produce CR the next day, which shows re- inactivation of the memory. The results represents that LTP could be reinstalling a memory of the shock or purely potentiating random inputs that causes lateral amygdala neurons to produce fear and reduce lever pressing. Also it provides a support to view LTP reactivation of memory that was formed by optical CS-shock pairing and causing inactivation by LTD.

To make sure the experiments that these scientists performed produce expected synaptic effects, they recorded the auditory region of lateral amygdala of rats expressing oChIEF in auditory regions. After gathering the data, the optical CS was not affected by the in vivo recording, which are depressed by optical LTD conditioning and potentiated by optical LTP conditioning. The results conclude that the synaptic stimulation modify synapses in the expected manner. Moreover, to find out more detailed relationship between synaptic stimulation conditioning protocols and memory processes, Nabavi and his colleague tested the effects of the protocols on “auditory cued-fear” conditioning. Overall, they concluded that LTP at auditory inputs to the amygdala could be necessary but not as effective to produce associative memory.

I believe that all the concepts including consolidation and reconsolidation are significant to memory and learning processes. Among those concepts, consolidation is the most valid concept whereas reconsolidation has similar validity but requires further research. I concur that reconsolidation can restructure memory. These concepts resonate with me greatly because the more they are studied and established, more people suffering from PTSD can be treated. However, there is always the question of ethics. It is always crucial to look at ethics when considering matters related to memory alteration. Moreover, even though there are a lot of neuroscientists and other brain related scientists performed many experiments related to consolidation, reconsolidation, and topics related to memory, I think it is necessary them to perform more experiments to ensure that they are comfortable and confident with the consequences and results that will bring.

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