The functional organization of visual cortical area 17/18 of the ferret was studied using a double-label 2-deoxyglucose (2-DG) method. Animals were stimulated sequentially with moving gratings of 2 different orientations. Elongated orientational patches running roughly at a right angle into the area 17/18 border were seen. The orientation maps were similar in areas 17 and 18. When animals were stimulated with 2 orthogonally oriented gratings, activation patterns were not fully complementary but did not overlap. A complex pattern of partial overlap was observed, with orientations differing by 45 degrees. More gradual and more abrupt changes alternated frequently on a scale smaller than the average periodicity in the patterns. A cortical patch representing a given orientation was regularly surrounded by both neighboring and orthogonal orientations. The direction of the orientational changes reversed frequently in the immediate vicinity of any orientational patch. Orientation maps were compared with complete maps of retino-cortical projections obtained by transneuronal labeling with intravitreally injected tritiated proline. Ocular dominance in the binocular segment of both areas 17 and 18 was found to be organized into elongated ipsilateral islands in an almost contiguous contralateral projection. In area 18, the patches were wider than in area 17, and the ipsilateral islands were smaller in the regions representing the upper and central visual field than in those representing the lower visual field.
An alternative method of estimating the lumped constant (LC) in the deoxyglucose model was developed. The LC was estimated using data obtained during the first 10 min after injection of the tracer by a nonlinear least-squares (NLSQ) method. The method does not require a constant plasma concentration. This approach was evaluated in a computer simulation by adding different levels of noise and considering various input functions. Errors in the estimated LC in this and Sokoloff et al.'s conventional method were compared. We found that the approach proposed here results in more reliable estimates of LC. The study in completed in a shorter experimental period, and any shape of the input function can be used. The new technique was then applied to measure whole brain LC and rate constants in cat brain for 2-[18F]fluoro-2-deoxy-D-glucose (2-[18F]FDG). Measured mean value (+/-s.e.m.) for the whole brain LC = 0.443 +/- 0.012 (N = 7), for the whole brain k2* = 0.124 +/- 0.009 and k3* = 0.024 +/- 0.001 (N = 7).
The expression of two cadherins, N- and R-cadherin, was mapped in the CNS of chicken embryos of 6–11 d incubation, focusing on the sensory and motor fiber systems. In the spinal cord, the laterally located fibers of the dorsal funiculus express N-cadherin while the medially located fibers do not. These two fiber systems have a different course within the CNS but associate to form the spinal dorsal roots. In the hindbrain, N-cadherin is expressed by the descending trigeminal (general somatic sensory) tract, which is contiguous with the N- cadherin-positive zone of the dorsal funiculus of the spinal cord. R- cadherin is not expressed by sensory fibers, but is expressed by the visceral motor system of the vagus and glossopharyngeal nerves, which are N-cadherin negative. The motor neurites expressing R-cadherin have a different course within the brain than the sensory neurites expressing N-cadherin, although they form the common sensory/motor roots of the vagus nerve at the surface of the brain. The possibility that N-cadherin provides a guidance cue for sensory axon migration within the CNS by a homophilic adhesion mechanism was investigated in vitro. Explants from sensory spinal ganglia expressing N-cadherin were placed on N-cadherin-transfected neuroblastoma cells, and axon outgrowth was visualized. Results showed that the sensory axons defasciculate and closely follow the cell-cell boundaries between transfected cells where high levels of N-cadherin are expressed. These results show that the two cadherins, like members of the immunoglobulin superfamily of molecules, are expressed in a topographically restricted fashion during chick brain development. They furthermore suggest that N- cadherin expression by neurites may play a role in guiding these neurites along CNS paths that express the same molecule.
This study investigates global properties of three categories of English text: canonical fiction, non-canonical fiction, and non-fictional texts. The central hypothesis of the study is that there are systematic differences with respect to structural design features between canonical and non-canonical fiction, and between fictional and non-fictional texts. To investigate these differences, we compiled a corpus containing texts of the three categories of interest, the Jena Corpus of Expository and Fictional Prose (JEFP Corpus). Two aspects of global structure are investigated, variability and self-similar (fractal) patterns, which reflect long-range correlations along texts. We use four types of basic observations, (i) the frequency of POS-tags per sentence, (ii) sentence length, (iii) lexical diversity, and (iv) the distribution of topic probabilities in segments of texts. These basic observations are grouped into two more general categories, (a) the lower-level properties (i) and (ii), which are observed at the level of the sentence (reflecting linguistic decoding), and (b) the higher-level properties (iii) and (iv), which are observed at the textual level (reflecting comprehension/integration). The observations for each property are transformed into series, which are analyzed in terms of variance and subjected to Multi-Fractal Detrended Fluctuation Analysis (MFDFA), giving rise to three statistics: (i) the degree of fractality ( ) of the fractal spectrum. The statistics thus obtained are compared individually across text categories and jointly fed into a classification model (Support Vector Machine). Our results show that there are in fact differences between the three text categories of interest. In general, lower-level text properties are better discriminators than higher-level text properties. Canonical fictional texts differ from non-canonical ones primarily in terms of variability in lower-level text properties. Fractality seems to be a universal feature of text, slightly more pronounced in non-fictional than in fictional texts. On the basis of our results obtained on the basis of corpus data we point out some avenues for future research leading toward a more comprehensive analysis of textual aesthetics, e.g., using experimental methodologies.
