Polyribosomal complexes beneath postsynaptic sites on dendrites provide a substrate for local translation of particular mRNAs, but the signals that target mRNAs to synapses remain to be defined. Here, we report that high frequency activation of the perforant path projections to the dentate gyrus causes newly synthesized mRNA for the immediate-early gene (IEG) Arc to localize selectively in activated dendritic segments. Newly synthesized Arc protein also accumulates in the portion of the dendrite that had been synaptically activated. The targeting of Arc mRNA was not disrupted by locally inhibiting protein synthesis, indicating that the signals for mRNA localization reside in the mRNA itself. This novel mechanism through which newly synthesized mRNA is precisely targeted to activated synapses is well suited to play a role in the enduring forms of activity-dependent synaptic modification that require protein synthesis.

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This article considers how experience can influence the developing and mature brain and proposes a new categorization scheme based upon the type of information stored and the brain mechanisms that appear to be involved in storing it. In this scheme, experience-expectant information storage refers to incorporation of environmental information that is ubiquitous in the environment and common to all species members, such as the basic elements of pattern perception. Experience-expectant processes appear to have evolved as a neural preparation for incorporating specific information: in many sensory systems, synaptic connections between nerve cells are overproduced, and a subsequent selection process occurs in which aspects of sensory experience determine the pattern of connections that remains. Experience-dependent information storage refers to incorporation of environmental information that is idiosyncratic, or unique to the individual, such as learning about one's specific physical environment or vocabulary. The neural basis of experience-dependent processes appears to involve active formation of new synaptic connections in response to the events providing the information to be stored. Although these processes probably do not occur entirely independently of one another in development, the categories offer a new view more in accord with neural mechanisms than were terms like "critical" or "sensitive period."

This article considers how experience can influence the developing and mature brain and proposes a new categorization scheme based upon the type of information stored and the brain mechanisms that appear to be involved in storing it. In this scheme, experience-expectant infonnation storage refers to incorporation of environmental information tliat is ubiquitous in the environment and common to all species members, such as the basic elements of pattem perception. Experience-expectant processes appear to have evolved as a neural preparation for incorporating speciBc infonnation: in many sensory systems, synaptic connections between nerve cells are overproduced, and a subsequent selection process occurs in which aspects of sensory experience determine the pattem of connections that remains. Experiencedependent infonnation storage refers to incorporation of environmental information that is idiosyncratic, or unique to the individual, such as leaming about one's specific physical environment or vocabulary. The neural basis of experience-dependent processes appears to involve active formation of new synaptic connections in response to tfie events providing the information to be stored. Although these processes probably do not occur entirely independently of one another in development, the categories oflfer a new view more in accord with neural mechanisms than were terms like "critical" or "sensitive period."