Although the N400 reflects stimulus-induced semantic activity in LTM, it does not necessarily follow that the activation states of the semantic memory system as a whole are strictly a function of the current input (eliciting stimulus) or, indeed, even of feed-forward stimulation in general. There is presumably always activity in the semantic system, and that activity is in constant flux in response to both external and internal events and states. For example, information that is encountered more often may tend to have higher baseline states of activity, and information that has been accessed recently – due to stimulus repetition or featural overlap – also will tend to be more active. Furthermore, activation states can be modulated by internally generated events, such as recalling a stimulus or predicting an upcoming one. Finally, a wide variety of state and trait-based factors – e.g., mood (Federmeier et al 2001), schizotypy (Kiang & Kutas 2005), etc. – as well as task demands and goals may change activity levels in semantic memory, at the global or more local levels, if not both. In all of
