Background:The possible causes of greater depression among adolescent girls were investigated by examining variation in the influence of genetic and environmental risk factors among 182 prepubertal female, 237 prepubertal male, 314 pubertal female, and 171 pubertal male twin pairs from the Virginia Twin Study of Adolescent Behavioral Development.

1. We recorded and tested quantitatively 65 middle temporal (MT) and 82 middle superior temporal (MST) cells in paralyzed and anesthetized monkeys. 2. Responses to the three elementary optic flow components (EFCs)--rotation, deformation, and expansion/contraction--and to translation (in the display) were compared after optimization of stimulus direction, speed, size, and position. As a control responses to flicker were measured. 3. Response windows were adapted in correspondence with our finding that latencies of MT and MST cells decrease with increasing speed for all types of motion. 4. There was a response continuum in MT as well as in MST cells. Compared with translation, MST cells responded significantly more to rotation but less to flicker than MT cells. MST cells were significantly more direction selective for expansion/contraction than MT cells. 5. MST cells generally responded to fewer motion types than MT cells. 6. Position invariance of EFC direction selectivity was tested over a region of the visual field centered on the translation receptive field (RF). Direction selectivity for an EFC was not position invariant in MT cells but it was invariant in 40% of the MST cells tested. These cells were considered EFC selective. 7. Most EFC-selective MST cells were selective for a single EFC, possibly combined with translation. Few of them were selective for deformation. 8. EFC selectivity was also speed invariant and EFC-selective MST cells usually had RFs summating inputs over wide portions of the visual field. 9. EFC-selective MST cells with similar selectivities were clustered.

Structural equation models were applied to the maternal ratings of 265 MZ and 163 DZ male-male, 347 MZ and 160 DZ female-female, and 262 male-female twin pairs, aged 8-16 years, who participated in the Virginia Twin Study of Adolescent Behavioral Development (VTSABD). Substantial additive genetic influences and contrast effects were found for hyperactivity, and additive genetic and shared environmental effects or positive comparison effects (particularly for the girls) for oppositional/ conduct disturbance. Bivariate model fitting showed that the covariation between hyperactivity and oppositional/conduct problems in both younger and older boys and girls is almost entirely attributable to genetic factors. However, whereas in the younger males and females the same set of genes explain all the variation in hyperactivity and conduct disturbance, in the older cohort at least some of the genetic effects are behavior- and gender-specific.

Optical flow is a rich source of information about the three-dimensional motion and structure of the visual environment. Little is known of how the brain derives this information. One possibility is that it analyzes first-order elementary components of optical flow, such as expansion, rotation, and shear. Using a combination of physiological recordings and modeling techniques, we investigated the contribution of the middle superior temporal area (MST), a third-order cortical area in the dorsal visual pathway that receives inputs from the medial temporal area (MT Optical flow, which can be defined as the apparent motion of the image brightness on the retina, has long been considered as a useful representation of visual motion information (1). According to a fundamental theorem of kinematics, or Helmholtz theorem (2), optical flow, within a small area of the visual field, can be seen as the sum of a translation with four elementary flow components (EFCs): a rotation (circular motion), an expansion (radial motion), and two components of shear (deformations) (3). This result has been successfully used in computer and computational vision for the analysis of motion (3-7). In addition, EFCs have been shown to be biologically relevant (8,9). Therefore, as suggested by recent studies in which middle superior temporal area (MST) cells of the monkey brain were reported to be selective for rotation and expansion (10-15), one may propose that the brain explicitly represents EFCs. MST is a third-order cortical area in the dorsal pathway leading to the parietal cortex (16). It receives inputs from the middle temporal area (MT) (17, 18), which has been implicated in motion analysis (19)(20)(21)(22), and is mainly driven by magnocellular input (23). However, there is disagreement about the degree of selectivity of MST cells: MST cells have been reported to be selective for a single EFC (10, 24) but also for several components (12, 13). Furthermore, there is no information about whether or not complex motion patterns are decomposed into the (linear) superposition of EFCs. Finally, it is not clear how the MST selectivity for EFCs is generated.Therefore, we quantitatively compared responses of cortical cells to translation and EFCs in both areas (MST and MT). To clearly distinguish between responses to local flow vectors and to global arrangements of vectors characteristic of EFCs, we systematically tested for the position invariance of the selectivity. Once selectivity for an EFC was established, we then studied the responses of MST cells to a combination of components, keeping one component constant. The results of the physiological study were used to model the transformations effected by the MST cells on MT input. METHODSWe have recorded from single MST and MT neurons of anesthetized and paralyzed monkeys (Macaca fascicularis) to obtain stable recordings over several hours and precisely localize the recorded units with respect to area and layer. The monkeys were anesthetized with sufentanil (5 pg-kg-1lh-1) and paralyze...

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