Word Frequency and brain activity

One of the basic forms of information that our brains are sensitive to, is the number of times we encounter an external event. This is most easily seen in examples of learning. Such as, the more we practice doing something, it becomes easier, we get faster at doing it, and even more accurate. Another example is that the more we encounter a specific information about an item or concept, we know a little more about it, maybe in a different way, maybe in a clearer way. Prior knowledge is updated.

The brain probably represents this frequency information in terms of changes in individual neuronal activity and inter-neuronal connectivity. In terms of internal neuronal changes, neurons may form more synapses that facilitate the generation of an action potential. There might also be reductions in synapses, leading to inhibitory type responses or de-potentiation. In terms of inter-neuronal connectivity, neurons may form more synapses with other neurons, axons may travel along certain paths in order to reach target brain regions, neuronal branching becomes more dense, or even less dense depending on the nature of the stimulation and connection. In all these cases, frequency of encountering stimuli, represented as frequency of individual neurons and networks of neurons being stimulated, leads to changes in neuronal structure and activity.

We start with an evaluation of how frequency of encountering words changes the way our brains respond when trying to access semantic information about those words. By semantic information, we typically refer to all associative information (neuronal connections) that are involved when we make an inclusion/exclusion categorizing judgment. In theory, we make these judgments by first evoking a set of semantic restrictions that define the target categories and keep this set active. We then identify the words, retrieve connections of these words, then match these retrieved connections to the active restriction set. This can proceed in a top-down/bottom-up competition type mechanism whereby bottom-up perceptual information about the word representation (lexical features, semantic associative strength and density) have to be resolved with the top-down imperative to match or not match the active semantic set relevant to the task.

In sum, the brain has to work harder for words encountered less frequently during such semantic judgments. Abstract: Frequency of concrete words modulates prefrontal activation during semantic judgments.

Perhaps, while low frequency should have fewer connections than high frequency words, since they have not had that much opportunity to form these connections due to the sparsity of their occurrence, the brain compensates their lack of obvious semantic associations by engaging more neuronal processing (particularly in the frontal regions). This may mark the recurrent search or matching effort to decide the category for the probe word.