Where in the Brain are Memories Formed?

The brain's memory centers
Anatomy of neurons and synapses
How memories are formed
Memory storage and consolidation
Memory retrieval and recollection
Memory disorders and neuroanatomy
Conclusion 
References
Further reading

Memory is often understood purely on a theoretical, cognitive basis. However, this perspective can only explain so much. Neuroanatomy offers an understanding of the physical areas of the brain in which these processes occur. Together, they form a part of cognitive neuroscience.

The brain can be studied on both a tissue and cellular level. Tissue makes up the structural elements of the brain, like the lobes, cortices, and periaqueductal grey matter. On a cellular level, a great deal of research focuses on the role of neurons.

The brain's memory centers

A number of different areas of the brain are associated with memory. Specifically, different areas are thought to have different specializations. For instance, one area of the brain may be associated with the creation of memory, while another is related to the consolidation of it. These areas work together to handle memory.

The hippocampus

The hippocampus is a significant area of the brain regarding memory and learning. It makes up a part of the temporal lobe and can be found next to the medial lobe.

Declarative memory and spatial reasoning are particular types of memory handled by this part of the brain. The hippocampus is especially significant to the encoding and retrieving allocentric spatial memory.

Allocentric spatial memory is a type of spatial orientation. Meaning ‘other-centred’, allocentric spatial memory relates to how people understand environments and recognize stimuli. The hippocampus seems to play a part in remembering the location of objects in relation to a particular perspective or point in space. However, the exact role it plays is unclear.

An experiment tested the spatial memory of participants with hippocampal damage using two cognitive tasks. Both tasks tested participants’ ability to recall and remember images from varying viewpoints. In one task, participants studied the locations of a few images before attempting to remember the images from the same and different viewpoints.

The results of the study suggested that the amount of information recalled may cause more issues than simply mentally changing the perspective or viewpoint. This suggests that the hippocampus may not impact viewpoint-related spatial memory as much, but instead, the capacity of spatial memory - and thus hippocampal damage limits this also.

The cerebral cortex

The cerebral cortex, also known as the neocortex, makes up over half of the volume of the brain. The scale of the cerebral cortex is thought to be due to the gyri spread across it,  which increases its overall surface area. It is associated with a wide range of functions, including thought, language, attention, and memory.

As the cerebral cortex is multifunctional, it is also instrumental in a range of different memory-related processes. One example of this is its role in phonological working memory, which is associated with auditory information. Phonological memory is crucial in speech and language perception.

One study investigated which areas of the brain related to the rehearsal of speech sounds and, therefore, phonological working memory, using a bank of experimental tasks. During the completion of the tasks, functional magnetic resonance imagery (fMRI) was used to measure the activity in the participants’ brains.

The study found increased activity across several areas of the cortex, particularly in areas associated with speech perception and production. There was a positive correlation between the number of phonological stimuli and levels of activity across the bilateral superior temporal and inferior frontal gyri and the supplementary motor area.

Anatomy of neurons and synapses

Neurons are a type of cell found in the brain. They communicate with electrochemical impulses, which dictate the cells’ behavior. These cells form the basis of a massive range of functions in the brain and the wider nervous system, including the formation and retention of memory.

Neurons communicate across the synapse: the space between one cell and the next. They do this through an electrical charge called the action potential. The action potential leads to a biochemical interaction, triggering the release of neurotransmitters into the synaptic gap. Neurotransmission is a building block of brain functioning and behavior.

A number of different neurotransmitters most likely play a fundamental role in the development, retention, and retrieval of memories. Dopamine, serotonin 5-HT, and glutamate are all associated with such processes. These neurotransmitters are all connected by gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter that triggers neuronal firing and, thus, neurotransmission.

How memories are formed

Cognitive processes are mostly used to explain the formation of memories. However, as they are theoretical concepts, it can be challenging - although not impossible - to demonstrate these theories empirically. Functional neuroanatomy and cognitive neuroscience offer an interdisciplinary way of attempting to measure these processes.

Episodic memory is one type of memory that has roots in functional neuroanatomy. Episodic memory is where the individual recalls where and when the memory was formed, often ‘seeing’ the memory play out cinematically.

Episodic memory has sensory encoding, meaning that the individual tends to remember sensory experiences from the event, such as the sights seen or sounds heard. Because of this, perceptual information that informs the creation of these memories appears to be handled by sensory areas of the brain.

The ventral medial temporal lobe creates representations of the episodic event. They’re then spread across different relevant cortical structures, such as the parahippocampal region of the brain and the perirhinal cortex.

Memory storage and consolidation

Any memory that is successfully formed and not forgotten enters storage. Consolidation occurs when memory is recorded in a more delible and ultimately retrievable way. This means that these memories become accessible through recall.

It is suggested that several different areas of the brain are involved in storage and consolidation, depending on the type of memory and the kind of information encoded to remember it. However, as many parts of the brain are flexible and multi-purposed, the hippocampal region is considered highly relevant to storing and consolidating multiple types of memory.

The hippocampal formation and cerebral cortex are thought to act together to consolidate episodic memory. Once information about the event that is being recorded has been gathered by the relevant cortices, it is then directed to the hippocampal formation by the Entorhinal Cortex. The hippocampal formation encodes the memory communicated to the cerebral cortex.

Memory retrieval and recollection

Retrieval happens when memory is recalled, making it immediately accessible again. This means that when someone remembers something, they retrieve the memory from a long or short-term memory store.

There is still a relative gap in the neurological understanding of memory retrieval. As ever, though, it appears that several areas could be related to the process. These areas include the hippocampus and the prefrontal lobe.

Much of the recent literature assesses the brain’s role in linguistic processing or language learning and, therefore, hinges mostly on phonological and semantic memory. Such research includes the investigation of word recall and lexical retrieval of those experiencing post-stroke aphasia, a group of language disorders with a neurocognitive underpinning.

Memory disorders and neuroanatomy

Memory disorders are a group of diagnoses that influence on the individual’s ability to create, store, recall, or otherwise process information. They include acute brain injuries, dementia disorders, and more.

Some experiences of traumatic brain injuries (TBI) may impact the working memory. Several studies have been conducted using fMRI to compare those with mild-to-moderate TBI to those without to assess the injuries’ impact on working memory. It seems that neural regions associated with working memory overlap with areas frequently vulnerable to injury.

The relatively common damage to substrate associated with working memory means that difficulties can be found in some aspects of working memory for those with TBI. Activating the working memory, as well as allocating resources to it, appear to both be areas of interest.

Conclusion

The brain is a highly specialized organ. Despite this, each area is significantly multi-functioned and multi-purposed, with each area handling a wide range of processes.

Specific areas of the brain seem to be prominent in forming, recalling, and storing memory. The hippocampus, for example, is an area that appears to handle a great deal of memory processes for several types of memory.

Neuroanatomical and physiological perspectives provide measurable insights into memory localization through neuroimaging methodologies. A significant volume of this research builds on cognitive psychology findings and theories, creating an inherently multidimensional perspective of memory.

To truly understand memory, a combination of approaches and perspectives is needed. Cognitive neuroscience helps to account for both theoretical perspectives and the structural underpinnings of memory found on both a tissue and cellular level.

References

• Shrager, Y., Bayley, P. J., Bontempi, B., Hopkins, R. O., & Squire, L. R. (2007). Spatial memory and the human hippocampus. Proceedings of the National Academy of Sciences, 104(8), 2961-2966.
• Bird, C. M., & Burgess, N. (2008). The hippocampus and memory: insights from spatial processing. Nature reviews neuroscience, 9(3), 182-194.
• Fidalgo, C., & Martin, C. B. (2016). The hippocampus contributes to allocentric spatial memory through coherent scene representations. Journal of Neuroscience, 36(9), 2555-2557.
• Fernandez‐Baizan, C., Nuñez, P., Arias, J. L., & Mendez, M. (2020). Egocentric and allocentric spatial memory in typically developed children: Is spatial memory associated with visuospatial skills, behavior, and cortisol?. Brain and Behavior, 10(5), e01532.
• Molnár, Z., Clowry, G. J., Šestan, N., Alzu'bi, A., Bakken, T., Hevner, R. F., ... & Kriegstein, A. (2019). New insights into the development of the human cerebral cortex. Journal of anatomy, 235(3), 432-451.
• Perrachione, T. K., Ghosh, S. S., Ostrovskaya, I., Gabrieli, J. D., & Kovelman, I. (2017). Phonological working memory for words and nonwords in cerebral cortex. Journal of Speech, Language, and Hearing Research, 60(7), 1959-1979.
• Caire, M. J., Reddy, V., & Varacallo, M. (2018). Physiology, synapse.
• Jewett, B. E., & Sharma, S. (2018). Physiology, GABA.
• Danieli, K., Guyon, A., & Bethus, I. (2023). Episodic Memory formation: A review of complex Hippocampus input pathways. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 110757.
• Meneses, A. (2014). Neurotransmitters and memory: cholinergic, glutamatergic, gabaergic, dopaminergic, serotonergic, signaling, and memory. In Identification of Neural Markers Accompanying Memory (pp. 5-45). Elsevier.
• McAllister, T. W., Flashman, L. A., McDonald, B. C., & Saykin, A. J. (2006). Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics. Journal of neurotrauma, 23(10), 1450-1467.
• Vakil, E. (2005). The effect of moderate to severe traumatic brain injury (TBI) on different aspects of memory: a selective review. Journal of clinical and experimental neuropsychology, 27(8), 977-1021.
• Depue, B. E. (2012). A neuroanatomical model of prefrontal inhibitory modulation of memory retrieval. Neuroscience & Biobehavioral Reviews, 36(5), 1382-1399.
• Markowitsch, H. J., & CALABRESE, P. (1999). Neuroanatomy of memory. In Neuronal Bases and Psychological Aspects of Consciousness (pp. 17-40).
• Wilmskoetter, J., Fridriksson, J., Gleichgerrcht, E., Stark, B. C., Delgaizo, J., Hickok, G., ... & Bonilha, L. (2019). Neuroanatomical structures supporting lexical diversity, sophistication, and phonological word features during discourse. NeuroImage: Clinical, 24, 101961.

Further Reading

• All Neuroscience Content
• What is Neurology?
• What is the Difference between Neurology and Neuroscience?
• What is Neuroscience?
• Implicit vs. Explicit Memories