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Adults and 8-month-olds were presented with sequences in which every third complex tone was either longer or more intense. Segmentation was measured by comparing the detection of silent gaps inserted into three possible locations in each pattern: Silent gaps inserted at perceived segmentation boundaries are harder to detect than gaps within perceived phrases or groups. A go/no-go conditioned head-tum (hand-raising for adults) procedure was used. In Experiment 1, detection was worse for the gaps following the longer complex tones than for the gaps at the other locations, suggesting that the longer tones marked the ends of perceived groups for both infants and adults. Experiment 2 showed that an increase in intensity did not result in any systematic grouping at either age.The perception ofspeech and music involves analyzing the structure ofa pattern or stream of sounds that unfolds in time. One of the basic steps in this process is the segmentation of the stream into meaningful units or groups, such as notes, words, and phrases. For adults, it is likely that the segmentation of both music and language involves the use ofboth structural and acoustic cues. Structural cues in language include grammatical rules and phonotactic constraints. For example, some phonemes or groups of phonemes are more likely to begin words, whereas others are more likely to end words. Structural cues in music include the functional relations between the different notes of the scale. For example, musical compositions most often end on the tonic, or first note, of the scale. The acoustic cues to phrase endings in both

Recurrent seizure activity induced during kindling has been reported to produce a functional synaptic reorganization of the mossy fibers in the hippocampus. To date, it is unclear whether this kindling-induced growth is secondary to decreases in hilar neuron density, which are presumed to reflect hilar neuronal cell loss, or whether it is related specifically to an activationdependent plasticity. We recently demonstrated that blocking nerve growth factor (NGF) biological activity retards seizure development and inhibits the sprouting of mossy fibers. We now demonstrate that intraventricular administration of NGF itself accelerates the progression of kindling epileptogenesis, increases mossy fiber sprouting in the CA3 region and in the inner molecular layer (IML), but reduces seizure-induced decreases in hilar cell density. These findings provide support for a role of NGF in kindling and kindling-induced mossy fiber sprouting. In addition, the results dissociate this form of epileptogenesis from hilar cell loss or decreases in hilar cell density attributable to increases in hilar area, thereby supporting seizure-induced mossy fiber sprouting as being primarily attributable to the combined effects of neuronal activation and the activation-induced upregulation of growth factors.

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