This blog post explores how the human brain stores and processes memories. We examine everything from the functioning of neurons and synapses to the storage locations for different types of memories.
Many scholars have strived to unravel the brain’s mysteries, yet the brain rarely reveals its true nature. If we could understand how and where the human brain stores memory information received from the outside world, wouldn’t we come closer to unlocking its secrets? However, solving this curiosity presents a far more complex and nuanced challenge than one might imagine. The brain is not a simple machine; its operation involves multidimensional processes that cannot be explained solely by electrical signals or chemical reactions. How the brain processes countless signals and stores various forms of memory remains an enigma.
While many theories have emerged recently about how memory information is stored in the brain, the most persuasive one suggests it occurs through physical and chemical changes in the synapses—the connection structures between neurons (nerve cells). The human brain contains approximately 100 billion neurons, each forming thousands of synapses to create a complex network. This network plays a crucial role in information storage and processing. A synapse consists of a presynaptic neuron that generates signals, a postsynaptic neuron that receives them, and the narrow gap between them—the synaptic cleft, approximately 20 to 50 nanometers wide. When an electrical signal is generated in the presynaptic neuron, neurotransmitters are released from its terminal into the synaptic cleft. These substances stimulate receptors on the postsynaptic neuron—the signal-receiving component—triggering the generation of an electrical signal. The brain functions because signals are transmitted through this neural network of synapses, enabling information processing. These complex synaptic interactions are one of the brain’s unique characteristics, and understanding them provides crucial clues to grasping the essence of memory and learning.
Memory information received by the brain is stored in different locations depending on its type. What we remember is broadly divided into declarative and non-declarative information. Declarative information is what can be expressed in words, such as school studies, movie plots, places or locations, and people’s faces. Non-declarative information, on the other hand, is information that cannot be expressed verbally, such as motor skills acquired through the body, habits, routines, and reflexive actions. Among these, the hippocampus, located in the medial temporal lobe of the brain, is known to play a crucial role in processing declarative information. This fact is supported by the example of a person whose declarative memory ability was impaired after suffering damage to the hippocampal region in a traffic accident. However, he recalled all his memories from before the accident. This suggests the hippocampus is not the storage site for long-term memory.
Many scholars propose the cerebral cortex as the location where declarative information is stored long-term. Declarative information entering the medial temporal lobe is fragmented and converted into neural signals during its temporary stay in the hippocampus and surrounding tissues, where decisions are made about how it will be divided and stored. The medial temporal lobe connects to extensive areas of the cerebral cortex and neural networks, transmitting this memory information to various regions of the cortex. Subsequently, memory-related genes are expressed, producing proteins that consolidate the memory content, maintaining it in a long-term stored state. This process involves not merely the accumulation of information but the continuous reorganization and strengthening of the brain’s neural networks, through which memories are vividly preserved.
So where is non-declarative information stored? Motor skills are stored in the brain’s striatum or cerebellum. Habituation, where one becomes desensitized to repeated stimuli, and sensitization, where one continues to respond to similar stimuli after initial exposure, are known to be stored in neural networks governing sensory or motor systems. Emotions or fear-related memories are stored in the amygdala. Thus, each region of the brain performs a unique role associated with specific memory types, demonstrating how intricately designed an organ the brain is.
Understanding these complex memory storage mechanisms goes beyond merely satisfying academic curiosity; it can also provide significant insights for treating neurological disorders or designing artificial intelligence systems. Research to unlock the brain’s secrets is still ongoing, and many challenges and discoveries await us in the future.
