Articles

Forgetting Mechanism: Neurogenesis as a Neurobiological Explanation

Abdulwahab F. Alahmari
Radiology Department, Al-Namas General Hospital, Ministry of Health, Al-Namas City, Saudi Arabia.

Article Info

Received Date: 21 June 2024, Accepted Date: 29 June 2024, Published Date: 02 July 2024

*Corresponding author: Abdulwahab F. Alahmari, Radiology Department, Al-Namas General Hospital, Ministry of Health, Al-Namas City, Saudi Arabia.

Citation:  Abdulwahab F. Alahmari (2024). “Forgetting mechanism: Neurogenesis as a neurobiological explanation”. International Journal of Case Reports and Case Research, 1(1); DOI: http;//doi.org/06.2024/IJCRCR/003.

Copyright: © 2024 Abdulwahab F. Alahmari. This is an open-access article distributed under the terms of the Creative Commons Attribution 4. 0 international License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

 

 Diagram 4. Warrington and Weiskrantz (1974) who described the implicit memory.

Diagram 5. Endel Tulving (1972) who described the explicit memory.

The prefrontal cortex, the hippocampus, the cerebellum, and the amygdala are the primary brain regions involved in memory. Declarative, episodic, and recognition memory are all linked to the hippocampus. The amygdala plays a role in fear and memories of terror. Processing procedural memories is mediated by the cerebellum. It indicates that remembering semantic activities involves the prefrontal cortex.   

Miller law in 1950s which indicates that the short-term memory is typically composed of 7 ± 2 items. The location of brain damage will reflect on which type of amnesia the patient will have whither anterograde vs. retrograde amnesia (Foster, 2008). Functional imaging is used to evaluate guilt or innocence of a potential convict. This is done by examining the ability of remembering that event which means the human personal memory privacy is at danger (Alahmari, 2021; Foster, 2008). Micro-disorientation in memory happens when someone forget their dreams which is common which a mechanism by the brain to allow the brain to focus on the reality (Fosse, 2001).

Infantile amnesia happens when young children do not remember previous life before 4 years of age which explained by the biological process as the maturity of hippocampus in 3-5 years of age (Goldman-Rakic, 1987). Even though, (Foster, 2008) claim it could be due to the shift in state of dependence, biological processes, or all of them together. 

Mathematical Analyses

There is no equivalent between brain’s memory capacity and computer’s memory capacity, so the scientists came with an idea that 1 bit = 1 synapse which is questionable. The brain has 250 trillion synapses which means 250 trillion bits. This means the brain capacity is 31.25 terabytes. 

In neuroscience there is a concept of “distributed representation” which means no single neuron have a memory for information, but neurons have information coded inside it as in the DNA. Why storing of information in a single neuron is not possible? Let’s say the distributed representation is true, how this distributed representation will give explanation of the forgetting mechanism? It does not give any answer and it will never be able to do it. The distributed representation could explain the foggy memory when the neuron that have information dies some parts of it’s information might still in the surrounding neurons which will give a foggy memory about a certain event.

But in other papers, they found that some cells called “place cells” when a rat run in maze, different cells fire to different part of the maze. This proves that memory of different places are stored in different cells which indicates that each neuron have memories of it’s own.

In one study, a mean of calculation of the numbers of neurons in 10 normal hippocampi show the average normal hippocampus contains 45.5 × 10⁵ neurons which means 48,500,000 (Šimić et al., 1997). The human brain contains two hippocampi which means (45.5 × 10⁵) × 2 = 97,000,000 is the average number of neurons in normal adults. The average volume of a normal hippocampus is 3.267 cm³ in one study, while another study reports 3.244 cm³ (Šimić et al., 1997; Mondragón et al., 2017). The average of these two studies is 3.2555 cm³. The brain memory capacity in normal adult human for information. One neuron can store only 1 bit. The human memory capacity is 2.5 petabytes (Reber, 2024). By following the previous numbers, the following calculation can be done.

In order to know how many neurons in 1 mm³ of the hippocampal formation tissue the volume change from cm to mm which is 3255.5 mm³. Then the number 48,500,000 of neurons is divided on 3255.5 mm³. The result will be 14,897.86 neurons in one mm³. Then these neurons each one will have one bit which means 1862.2325 bytes. If 1 mm³ get damaged or shrink of the hippocampus then 1862.2325 bytes of information will be lost. The two hippocampi will have the capacity of 1,2125,000 bytes which is 0.012125 gigabytes. By this simple calculation, which show the hippocampi are not the only memory areas in the brain.

If we convert the 2.5 petabytes to bytes it will be 2,814,749,767,106,560 bytes then we divide this number on the number neurons in both hippocampi it will show that the memory capacity is 29,018,038.83 bytes per neuron which is 29.01 megabytes which is a small part of CD (i.e. 6.7%). Since one Compact Disc (CD) is 700 megabytes. This shows that this is does not seem logical calculations for being too high.

The total number of neurons in the brain is 86 billion neurons (Herculano-Houzel, 2009). If we divide the memory capacities in bits (232144310.64) on the whole number of neurons in the brain 86 billion neurons then each neuron will have the memory capacity of 0.00269935244 bits (i.e. less than one bit). This calculation does not seem right for being too low.

If we calculate the total numbers neurons in the 4 locations in the brain that are responsible for memory which are prefrontal cortex, the hippocampus, the cerebellum, and the amygdala. The total number of neurons the prefrontal cortex is 1,280,000,000 neurons (Gabi, 2016). The total number neurons in the cerebellum is 69,000,000,000 (Herculano-Houzel, 2009). The total number of neurons in two hippocampi is 97,000,000 neurons (Šimić et al., 1997). The total number of neurons in one amygdala is 12.75 million then the number is multiple by 2 for having two amygdala in the brain that make 25,500,000 neurons. The total number of neurons is 70,402,500,000 cells. If we divide 2,814,749,767,106,560 bytes by total number of neurons in the 4 for mentioned area (i.e. 70,402,500,000) will equal 39,980.82 bytes per cell. This means one neuron will have the capacity of 39.98 kilobytes. The capacity of one neuron is near half of the first floppy disc ever invented which has size of 80 kilobytes. 

In the human’s memory, when a cell dies that is losing a small part of the bit of information. When there is a bigger loss of neurons, then bits combine to form a byte (1 byte consists of 8 bits). Then memory get lost.

There is a hypothesis called “the frontal lobe hypothesis” (West, 1996). This hypothesis suggests that the degeneration of the frontal lobe cause age related memory loss (Foster, 2008), which indicates that there are other storage areas of memories outside the hippocampi. The frontal lobe matures late around 20 years of age and the frontal lobe deteriorate early in adults which result in affecting the strategic and organizational aspect of memory. Decline in brain capacity has a hallmark as frontal lobe atrophy which results in Mild Cognitive Impairment (MCI). It has been postulated that MCI could be specific amnestic MCI or multiple cognitive domain MCI.

According to Koob (2009), the cortical memory is abolished by blocking the glutamate reuptake. Yet researchers were not able to know how the cortex contains information (Koob, 2009).