As an adult, upon hearing the same word you may well picture your own house-a different response for the same input. The theory is that strengthening or weakening synapses makes particular patterns of neuronal activity more or less likely to occur.Īs a five-year-old, if given the word 'house', you might have imagined a drawing of a house. If you think of your cat, or your home, or your fifth birthday cake, different ensembles, or groups, of neurons become active. In the brain, any stimulus results in a particular pattern of neuronal activity-certain neurons become active in more or less a particular sequence. Memories occur when specific groups of neurons are reactivated. Different 'neuron ensembles' for different memories In humans, exercise has been shown to increase the volume of the hippocampus – suggesting new neurons are being created – and at the same time improve performance in memory tasks. Studies in older mice have shown that by increasing neurogenesis in the hippocampus, memory can be improved. In some parts of the adult brain, such as the important memory structure known as the hippocampus, brand new neurons can be created in a process called neurogenesis. But there is also evidence that another type of plasticity, not directly involving synapses, could be important for memory formation. Lasting increases and decreases in synaptic strength are called long-term potentiation (LTP) and long-term depression (LTD).Ĭhanging the strength of existing synapses, or even adding new ones or removing old ones, is critical to memory formation. Active connections tend to get stronger, whereas those that aren’t used get weaker and can eventually disappear entirely.Ī connection between two neurons becomes stronger when neuron A consistently activates neuron B, making it fire an action potential (spike), and the connection gets weaker if neuron A consistently fails to make neuron B fire a spike.
These connections can be made stronger or weaker depending on when and how often they have been activated in the past. This term describes the persistent changes in the strength of connections – called synapses – between brain cells. But what allows a specific combination of neurons to be reactivated over any other combination of neurons? Memory is the reactivation of a specific group of neurons, formed from persistent changes in the strength of connections between neurons. Different groups of neurons (nerve cells), responsible for different thoughts or perceptions, drift in and out of action.
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