The relationship between diurnal type and time duration estimation at morning and evening times of day

This study investigates whether different diurnal types (morning versus evening) differ in their estimation of time duration at different times of the day. Given that the performance of morning and evening types is typically best at their preferred times of day, and assuming different diurnal trends in subjective alertness (arousal?) for morning and evening types, and adopting the attentional gate model of time duration estimation, it was predicted that morning types would tend to underestimate and be more accurate in the morning compared to evening types where the opposite pattern was expected. Nineteen morning types, 18 evening types and 18 intermediate types were drawn from a large sample (N=1175) of undergraduates administered the Early/Late Preference Scale. Groups performed a time duration estimation task using the production method for estimating 20-s unfilled intervals at two times of day: 0800/1830. The median absolute error, median directional error and frequency of under- and overestimation were analysed using repeated-measures ANOVA. While all differences were statistically non-significant, the following trends were observed: morning types performed better than evening types; participants overestimated in the morning and underestimated in the evening; and participants were more accurate later in the day. It was concluded that the trends are inconsistent with a relationship between subjective alertness and time duration estimation but consistent with a possible relationship between time duration estimation and diurnal body temperature fluctuations. (C) 2002 Elsevier Ltd. All rights reserved.

Spreading and synchronization of intrinsic signals in visual cortex of macaque monkey evoked by a localized visual stimulus

Spatio-temporal maps of the occipital cortex of macaque monkeys were analyzed using optical imaging of intrinsic signals. The images obtained during localized visual stimulation (IS) were compared with the images obtained on presentation of a blank screen (IB). We first investigated spontaneous variations of the intrinsic signals by analyzing the 100 IBs for each of the three cortical areas. Slow periodical activation was observed in alternation over the cortical areas. Cross-correlation analysis indicated that synchronization of spontaneous activation only took place within each cortical area, but not between them. When a small, drifting grating (2degreesX2degrees) was presented on the fovea. a dark spot appeared in the optical image at the cortical representation of this retinal location. It spread bilaterally along the border between V1 and V2, continuing as a number of parallel dark bands covering a large area of the lateral surface of V1. Cross-correlation analysis showed that during visual stimulation the intrinsic signals over all of the three cortical areas were synchronized, with in-phase activation of V1 and V2 and anti-phase activation of V4 and V1/V2. The significance of these extensive synergistic and antagonistic interactions between different cortical areas is discussed. (C) 2003 Elsevier B.V. All rights reserved.

A study of pyramidal cell structure in the cingulate cortex of the macaque monkey with comparative notes on inferotemporal and primary visual cortex

Recent studies have revealed a marked degree of variation in the pyramidal cell phenotype in visual, somatosensory, motor and prefrontal cortical areas in the brain of different primates, which are believed to subserve specialized cortical function. In the present study we carried out comparisons of dendritic structure of layer III pyramidal cells in the anterior and posterior cingulate cortex and compared their structure with those sampled from inferotemporal cortex (IT) and the primary visual area (V1) in macaque monkeys. Cells were injected with Lucifer Yellow in flat-mounted cortical slices, and processed for a light-stable DAB reaction product. Size, branching pattern, and spine density of basal dendritic arbors was determined, and somal areas measured. We found that pyramidal cells in anterior cingulate cortex were more branched and more spinous than those in posterior cingulate cortex, and cells in both anterior and posterior cingulate were considerably larger, more branched, and more spinous than those in area V1. These data show that pyramidal cell structure differs between posterior dysgranular and anterior granular cingulate cortex, and that pyramidal neurons in cingulate cortex have different structure to those in many other cortical areas. These results provide further evidence for a parallel between structural and functional specialization in cortex.

First- and second-order stimulus length selectivity in New World monkey striate cortex

Motion is a powerful cue for figure-ground segregation, allowing the recognition of shapes even if the luminance and texture characteristics of the stimulus and background are matched. In order to investigate the neural processes underlying early stages of the cue-invariant processing of form, we compared the responses of neurons in the striate cortex (V1) of anaesthetized marmosets to two types of moving stimuli: bars defined by differences in luminance, and bars defined solely by the coherent motion of random patterns that matched the texture and temporal modulation of the background. A population of form-cue-invariant (FCI) neurons was identified, which demonstrated similar tuning to the length of contours defined by first- and second-order cues. FCI neurons were relatively common in the supragranular layers (where they corresponded to 28% of the recorded units), but were absent from layer 4. Most had complex receptive fields, which were significantly larger than those of other V1 neurons. The majority of FCI neurons demonstrated end-inhibition in response to long first- and second-order bars, and were strongly direction selective, Thus, even at the level of V1 there are cells whose variations in response level appear to be determined by the shape and motion of the entire second-order object, rather than by its parts (i.e. the individual textural components). These results are compatible with the existence of an output channel from V1 to the ventral stream of extrastriate areas, which already encodes the basic building blocks of the image in an invariant manner.

Specialization in pyramidal cell structure in the sensory-motor cortex of the vervet monkey (Cercopethicus pygerythrus)

Recent studies have revealed systematic differences in the pyramidal cell structure between functionally related cortical areas of primates. Trends for a parallel in pyramidal cell structure and functional complexity have been reported in visual, somatosensory, motor, cingulate and prefrontal cortex in the macaque monkey cortex. These specializations in structure have been interpreted as being fundamental in determining cellular and systems function, endowing circuits in these different cortical areas with different computational power. In the present study we extend our initial finding of systematic specialization of pyramidal cell structure in sensory-motor cortex in the macaque monkey [Cereb Cortex 12 (2002) 1071] to the vervet monkey. More specifically, we investigated pyramidal cell structure in somatosensory and motor areas 1/2, 5, 7, 4 and 6. Neurones in fixed, flat-mounted, cortical slices were injected intracellularly with Lucifer Yellow and processed for a light-stable 3,3'-diaminobenzidine reaction product. The size of, number of branches in, and spine density of the basal dendritic arbors varied systematically such that there was a trend for increasing complexity in arbor structure with progression through 1/2, 5 and 7. In addition, cells in area 6 were larger, more branched, and more spinous than those in area 4. (c) 2005 IBRO. Published by Elsevier Ltd. All rights reserved.

Pyramidal cell specialization in the occipitotemporal cortex of the vervet monkey

Pyramidal cells were injected intracellularly in fixed, flat-mounted cortical slices taken from the first and fourth visual areas (VI and V4, respectively) and cytoarchitectonic areas TEO and TE of two age and gender-matched vervet monkeys and the size, branching complexity and spine density of their basal dendritic trees determined. In both animals, we found marked differences in the pyramidal cell phenotype between cortical areas. More specifically, a consistent trend for larger, more branched and more spinous pyramidal cells with progression through VI, V4, TEO and TE was observed. These findings support earlier reports of interareal specialization in pyramidal cell structure in occipitotemporal visual areas in the macaque monkey. (c) 2005 Lippincott Williams & Wilkins.

Resolving the organization of the New World monkey third visual complex: The dorsal extrastriate cortex of the marmoset (Callithrix jacchus)

We tested current hypotheses on the functional organization of the third visual complex, a particularly controversial region of the primate extrastriate cortex. In anatomical experiments, injections of retrograde tracers were placed in the dorsal cortex immediately rostral to the second visual area (V2) of New World monkeys (Callithrix jacchus), revealing the topography of interconnections between the third tier cortex and the primary visual area (V1). The data indicate the presence of a dorsomedial area (DM), which represents the entire upper and lower quadrants of the visual field, and which receives strong, topographically organized projections from the superficial layers of V1. The visuotopic organization and boundaries of DM were confirmed by electrophysiological recordings in the same animals and by architectural characteristics which were distinct from those found in ventral extrastriate cortex rostral to V2. There was no electrophysiological or histological evidence for a transitional area between V2 and DM. In particular, the central representation of the upper quadrant in DM was directly adjacent to the representation of the horizontal meridian that marks the rostral border of V2. The present results argue in favor of the hypothesis that the third visual complex in New World monkeys contains different areas in its dorsal and ventral components: area DM, near the dorsal midline, and a homolog of area 19 of other mammals, located more lateral and ventrally. The characteristics of DM suggest that it may correspond to visual area 6 (V6) of Old World monkeys. (C) 2005 Wiley-Liss, Inc.

Regional specialization in pyramidal cell structure in the limbic cortex of the vervet monkey (Cercopithecus pygerythrus): an intracellular injection study of the anterior and posterior cingulate gyrus

The pyramidal cell phenotype varies quite dramatically in structure among different cortical areas in the primate brain. Comparative studies in visual cortex, in particular, but also in sensorimotor and prefrontal cortex, reveal systematic trends for pyramidal cell specialization in functionally related cortical areas. Moreover, there are systematic differences in the extent of these trends between different primate species. Recently we demonstrated differences in pyramidal cell structure in the cingulate cortex of the macaque monkey; however, in the absence of other comparative data it remains unknown as to whether the neuronal phenotype differs in cingulate cortex between species. Here we extend the basis for comparison by studying the structure of the basal dendritic trees of layer III pyramidal cells in the posterior and anterior cingulate gyrus of the vervet monkey (Brodmann's areas 23 and 24, respectively). Cells were injected with Lucifer Yellow in flat-mounted cortical slices, and processed for a light-stable DAB reaction product. Size, branching pattern, and spine density of basal dendritic arbors were determined, and somal areas measured. As in the macaque monkey, we found that pyramidal cells in anterior cingulate gyrus (area 24) were more branched and more spinous than those in posterior cingulate gyrus (area 23). In addition, the extent of the difference in pyramidal cell structure between these two cortical regions was less in the vervet monkey than in the macaque monkey.

Diurnal polyp expansion behavior in stony corals may enhance carbon availability for symbionts photosynthesis

Photosynthesis of zooxanthellate stony corals may be limited by inorganic carbon at high irradiances. We demonstrated that oxygen consumption of expanded corals is higher than that of contracted corals in both night-expanding and day-expanding corals. It is assumed that at the single-polyp level, the expansion of tentacles increases the surface area for solute exchange with the surrounding water, which may alleviate potential carbon limitation and excess oxygen levels in the tissue under high irradiance. We investigated this hypothesis using stable carbon isotope (613 C) analysis of coral species from the Red Sea exhibiting different morphologies. delta C-13 ratios in zooxanthellae of branched coral colonies with small polyp size that extend their tentacles during daytime (diurnal morphs) showed lower delta C-13 values in their zooxanthellae - 13.83 +/- 1.45 parts per thousand, compared to corals from the same depth with large polyps, which are usually massive and expand their tentacles only at night (nocturnal morphs). Their algae delta C-13 was significantly higher, averaging - 11.33 +/- 0.59 parts per thousand. Carbon isotope budget of the coral tissue suggests that branched corals are more autotrophic, i.e., that they depend on their symbionts for nutrition compared to massive species, which are more heterotrophic and depend on plankton predation. (c) 2005 Elsevier B.V. All rights reserved.

Specialization of pyramidal cell structure in the visual areas V1, V2 and V3 of the South American rodent, Dasyprocta primnolopha

Marked phenotypic variation has been reported in pyramidal cells in the primate cerebral cortex. These extent and systematic nature of these specializations suggest that they are important for specialized aspects of cortical processing. However, it remains unknown as to whether regional variations in the pyramidal cell phenotype are unique to primates or if they are widespread amongst mammalian species. In the present study we determined the receptive fields of neurons in striate and extrastriate visual cortex, and quantified pyramidal cell structure in these cortical regions, in the diurnal, large-brained, South American rodent Dasyprocta primnolopha. We found evidence for a first, second and third visual area (V1, V2 and V3, respectively) forming a lateral progression from the occipital pole to the temporal pole. Pyramidal cell structure became increasingly more complex through these areas, suggesting that regional specialization in pyramidal cell phenotype is not restricted to primates. However, cells in V1, V2 and V3 of the agouti were considerably more spinous than their counterparts in primates, suggesting different evolutionary and developmental influences may act on cortical microcircuitry in rodents and primates. (c) 2006 Elsevier B.V. All rights reserved.