Information on normal functional organization and development of the ventral processing stream in 5-to 11-year-old children is minimal. The present fMRI study identified neural correlates for face and object processing in children aged 5-8 and 9-11 years, with data from a similar adult study used for comparison. All age groups showed face-preferential activation in the ventral processing stream, but adults and children aged 9-11 years showed face-preferential loci near the classically defined fusiform face area, whereas children aged 5-8 years showed this activation in the posterior ventral processing stream. In addition, the degree of category-selectivity in other brain regions increased with age. Collectively, these developmental changes may reflect finetuning in visual recognition processes based on learning and experience.

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The present study explored constraints on mid-fusiform activation during object discrimination. In three experiments, participants performed a matching task on simple line configurations, nameable objects, three dimensional (3-D) shapes, and colors. Significant bilateral mid-fusiform activation emerged when participants matched objects and 3-D shapes, as compared to when they matched two-dimensional (2-D) line configurations and colors, indicating that the mid-fusiform is engaged more strongly for processing structural descriptions (e.g., comparing 3-D volumetric shape) than perceptual descriptions (e.g., comparing 2-D or color information). In two of the experiments, the same mid-fusiform regions were also modulated by the degree of structural similarity between stimuli, implicating a role for the mid-fusiform in fine differentiation of similar visual object representations. Importantly, however, this process of fine differentiation occurred at the level of structural, but not perceptual, descriptions. Moreover, mid-fusiform activity was more robust when participants matched shape compared to color information using the identical stimuli, indicating that activity in the mid-fusiform gyrus is not driven by specific stimulus properties, but rather by the process of distinguishing stimuli based on shape information. Taken together, these findings further clarify the nature of object processing in the mid-fusiform gyrus. This region is engaged specifically in structural differentiation, a critical component process of object recognition and categorization.

In the present object recognition study, we examined the relationship between brain activation and four behavioral measures: error rate, reaction time, observer sensitivity, and response bias. Subjects perceptually matched object pairs in which structural similarity (SS), an index of structural differentiation, and exposure duration (DUR), an index of task difficulty, were manipulated. The SS manipulation affected the fMRI signal in the left anterior fusiform and parietal cortices, which in turn reflected a bias to respond same. Conversely, an SS-modulated fMRI signal in the right middle frontal gyrus reflected a bias to respond different. The DUR manipulation affected the fMRI signal in occipital and posterior fusiform regions, which in turn reflected greater sensitivity, longer reaction times, and greater accuracy. These findings demonstrate that the regions most strongly implicated in processing object shape (SS-modulated regions) are associated with response bias, whereas regions that are not directly involved in shape processing are associated with successful recognition performance.

Lampreys belong to the Agnathans, the sister group of jawed vertebrates. Accordingly, characterization of neuronal groups and their development may provide useful information for understanding early evolution of the vertebrate nervous system. Here, the development of the CNS serotonergic system of the sea lamprey from embryos to adults was investigated immunocytochemically with an antibody against serotonin. The appearance of the different serotonin-immunoreactive neuronal populations occurs between the embryonic and metamorphic stages. The earliest serotonergic neurons appear in the basal plate of the isthmus of late embryos. In prolarvae, there appear progressively new serotonergic cell groups: first in the spinal cord, followed by those of the pineal organ, tuberal region, zona limitans intrathalamica, and then in the caudal rhombencephalon. In early larvae, a new serotonergic population appears in the mammillary region, whereas serotonergic cells of the pretectal region and parapineal organ first appear in middle and late larval stages, respectively. The first serotonergic fibers grow in early prolarvae, ascending and descending from the isthmic cell group, and the number of immunoreactive fibers progressively increases until the adult period. During metamorphosis, serotonin-immunoreactive cells appear in the retina. Comparison of the spatiotemporal sequence of appearance of serotonergic cells in agnathans and gnathostomes stresses the evolutionary trend for disappearance of rostral serotonergic cell groups in tetrapods, and for increase of differentiated groups in the brainstem. It also reveals that the developmental pattern of early ascending and descending serotonergic pathways is remarkably similar among vertebrates. Some striking differences between development of serotonergic structures in lampreys and other vertebrates are in close relation to the peculiar development of the lamprey visual system.