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PubMed2002

Passive avoidance training enhances cell proliferation in 1-day-old chicks.

One-day-old domestic chicks were injected i.p. with bromodeoxyuridine (BrdU) before training on a one-trial passive avoidance task where the aversive experience was a bead coated with a bitter tasting substance, methyl anthranilate (MeA). Animals were tested 24 h later; those avoiding (if MeA-trained) or pecking if water (W)-trained (which they peck appetitively), along with a group of untrained naïve chicks, were used to determine cell proliferation either 24 h or 9 days post BrdU injection. In all three groups, BrdU positive cells were identified sparsely throughout the forebrain but labelling was pronounced around ventricular zone (VZ) surfaces at both 24 h and 9 days post-BrdU-injection. Double immunolabelling with neuronal specific antibodies, to either NeuN, or beta-tubulin III, confirmed that most BrdU labelled cells appeared to be neurons. Unbiased stereological analysis of labelled cells in selected forebrain areas 24 h post BrdU injection showed a significant MeA-training induced increase in labelled cells in both the dorsal VZ surface bordering the intermediate and medial hyperstriatum ventrale (IMHV) and the tuberculum olfactorium (TO). By 9 days post-BrdU-injection, there was a significantly greater number of BrdU labelled cells in MeA-trained birds within the IMHV, lobus parolfactorius (LPO) and TO. These results demonstrate that avoidance training in 1-day-old chicks has a marked effect on cell proliferation, in the LPO and IMHV, regions of the chick previously identified as a key loci of memory formation, and in a second region (TO), which has olfactory functions, but has not been previously investigated in relation to avoidance learning.

Animals↗
PubMed2002

Laboratory practice at the periphery in developing countries.

An effective national health service structure requires a comprehensive programme for primary health care in peripheral and rural areas. This is especially important in under-resourced countries where facilities are sparse, the population is widely dispersed and transport is limited. Haematology has a key role in diagnosis and patient management by selecting tests for their clinical relevance and utility for the specific circumstances, and ensuring their technical reliability when used in health clinics and point-of-care testing. WHO has proposed a basic menu of tests in three categories: (a) tests such as haemoglobin screen which can be performed by nurses, midwives, health-aides or community doctors, (b) tests such as haemoglobinometry, microhaematocrit and microscopic examination of stained preparations which can be performed by a technician or laboratory assistant in a health centre, (c) tests requiring greater technical expertise of a laboratory technician or trained doctor. The peripheral health clinics and district laboratories must be familiar with the guidelines on standardized methods for collecting and storing specimens and transporting them to a regional laboratory or a reference centre. A training syllabus should be provided at the health centres and district laboratories, and this should include on-site instruction from supervisors and access to training manuals and distance-learning material. A co-ordinated programme of quality assurance and standardization of test methods should be established by a reference centre or national health authority with a network which encompasses all laboratories and health clinics undertaking any tests. Each regional laboratory should foster lower level laboratories or clinics within its neighbourhood. Of particular concern is the reliable diagnosis and management of anaemia. WHO reports indicate that 40% of the world population suffer from anaemia, especially affecting pregnant women, and a high proportion of infants and children in developing countries. The Haemoglobin Colour Scale (HCS) was recently developed for WHO as a simple, cheap and portable device which reads haemoglobin within 1 g/dl of the true value. It has been validated in a number of studies and is now manufactured commercially in accordance with WHO specifications under control of a WHO Collaborating Centre. It has an important potential role in the resource-limited environment where anaemia screening presently usually depends on unreliable clinical examination.

Anemia↗
PubMed2004

Immunocytochemical localization of GABABR1 receptor subunits in the basolateral amygdala.

Gamma-aminobutyric acid B (GABAB) receptors (GBRs) are G-protein-coupled receptors that mediate a slow, prolonged form of inhibition in the basolateral amygdala (ABL) and other brain areas. Recent studies indicate that this receptor is a heterodimer consisting of GABABR1 (GBR1) and GABABR2 subunits. In the present investigation, antibodies to the GABABR1 subunit were used to study the neuronal localization of GBRs in the rat ABL. GBR immunoreactivity was mainly found in spine-sparse interneurons and astrocytes at the light microscopic level. Very few pyramidal neurons exhibited perikaryal staining. Dual-labeling immunofluorescence analysis indicated that each of the four main subpopulations of interneurons exhibited GBR immunoreactivity. Virtually 100% of large CCK+ neurons in the basolateral and lateral nuclei were GBR+. In the basolateral nucleus 72% of somatostatin (SOM), 73% of parvalbumin (PV) and 25% of VIP positive interneurons were GBR+. In the lateral nucleus 50% of somatostatin, 30% of parvalbumin and 27% of VIP positive interneurons were GBR+. Electron microscopic (EM) analysis revealed that most of the light neuropil staining seen at the light microscopic level was due to the staining of dendritic shafts and spines, most of which probably belonged to spiny pyramidal cells. Very few axon terminals (Ats) were GBR+. In summary, this investigation demonstrates that the distal dendrites of pyramidal cells, and varying percentages of each of the four main subpopulations of interneurons in the ABL, express GBRs. Because previous studies suggest that GBR-mediated inhibition modulates NMDA-dependent EPSPs in the ABL, these receptors may play an important role in neuronal plasticity related to emotional learning.

Amygdala↗
PubMed2003

Stereoscopic surface interpolation supports lightness constancy.

The human visual system has a remarkable ability to construct surface representations from sparse stereoscopic, as well as texture and motion, information. In impoverished displays where few points are used to define regions in depth, the brain often interpolates depth estimates across intervening blank regions to create a compelling sense of a solid surface. The set of experiments described here examined stereoscopic interpolation using a novel technique based on lightness constancy. The effectiveness of this method is notable because it stands as the only technique to date that unequivocally examines the perception of interpolated surfaces, and not surfaces inferred subjectively from depth information in the stimulus. Further, these data support the growing evidence that a primary function of the stereoscopic system is to define three-dimensional surface structure.

Adult↗
PubMed2002

Volatile visual representations: failing to detect changes in recently processed information.

Research documenting people's inability to detect large changes in visual scenes suggests that visual representations may be sparse and volatile, providing no cumulative record of the attended items in a scene. However, these studies have failed to control for attention. Thus, the visual system may construct a cumulative record of all attended stimuli and still miss such changes, because they involve items that were never attended to. In two experiments, subjects saw 12-digit arrays and identified either the highest digit in the array (Experiment 1) or the lowest digit not in the array (Experiment 2). Subsequent change-detection tasks revealed that subjects often failed to detect changes that involved the same digits they had previously identified to perform the digit tasks successfully. This provides additional evidence that our usable visual representations are relatively impoverished and volatile.

Adult↗
PubMed2003

Laparoscopic orchiopexy: report of 203 cases with review of diagnosis, operative technique, and lessons learned.

BACKGROUND AND PURPOSE: Proper management of the nonpalpable testicle requires an accurate diagnosis. Laparoscopic orchiopexy (LO) has become the standard for diagnosis and treatment. We classified the location of nonpalpable testicles, reviewed the technique of LO in detail, and report the results of our series, the largest described to date. PATIENTS AND METHODS: We compiled the records of all cryptorchid patients seen between 1994 and 2002. Those with testicles located near the internal inguinal ring and those with nonpalpable testicles underwent laparoscopy and LO in the same session. The 173 patients underwent 203 procedures, all performed by the senior authors. RESULTS: The undescended testicles were right-sided in 33% of patients, left-sided in 53%, and bilateral in 14%. Six testicles were excluded because of hypotrophy (N=4) or agenesis of the vas deferens (N=2). At laparoscopy, 58% of the testicles were at the iliac vessels or higher (high intra-abdominal), 22% were between the iliac vessels and the internal ring (low intra-abdominal), 16% were peeping, 3% were intracanicular, and 1% were retrovesical. Standard LO was performed in 70.5% of the patients, with the remainder being treated by laparoscopic Fowler-Stephens orchiopexy. There have been four cases of testicular atrophy, all after Fowler-Stephens procedures. Two were virgin gonads, and the other two had previously been subjected to extensive orchiolysis. Only 3% of the patients required repeat surgery because of an unsatisfactory testicular location. CONCLUSION: The reported success rate for LO of intra-abdominal testicles has far exceeded that of open repair (95% v 76%). It is our belief that minimal manipulation of the testicle during dissection, a wider peritoneal window, and sparse use of electrocautery will result in adequate testicular position even for high intra-abdominal gonads with minimal risk of atrophy.

Atrophy↗
PubMedDate not supplied

Pattern separation and synchronization in spiking associative memories and visual areas.

Scene analysis in the mammalian visual system, conceived as a distributed and parallel process, faces the so-called binding problem. As a possible solution, the temporal correlation hypothesis has been suggested and implemented in phase-coding models. We propose an alternative model that reproduces experimental findings of synchronized and desynchronized fast oscillations more closely. This model is based on technical considerations concerning improved pattern separation in associative memories on the one hand, and on known properties of the visual cortex on the other. It consists of two reciprocally connected areas, one corresponding to a peripheral visual area (P), the other a central association area (C). P implements the orientation-selective subsystem of the primary visual cortex, while C was modeled as an associative memory with connections formed by Hebbian learning of all assemblies corresponding to stimulus objects. Spiking neurons including habituation and correlated noise were incorporated as well as realistic synaptic delays. Three learned stimuli were presented simultaneously and correlation analysis was performed on spike recordings. Generally, we found two states of activity: (i) relatively slow and unordered oscillations at about 20-25 Hz, synchronized only within small regions; and (ii) faster and more precise oscillations around 50-60 Hz, synchronized over the whole simulated area. The neuron groups representing one stimulus tended to be simultaneously in either the slow or the fast state. At each particular time, only one assembly was found to be in the fast state. Activation of the three assemblies switched on a time scale of 100 ms. This can be interpreted as self-generated attention switching. On the time scale corresponding to gamma oscillations, cross correlations between local neuron groups were either modulated or flat. Modulated correlograms resulted if the groups coded features corresponding to a common object. Otherwise, the correlograms remained flat. This behavior is in agreement with experimental results, while phase-code models would generally predict modulated correlations also in the case of different objects. Furthermore, we derive a technical version from our biological associative memory model that accomplishes fast pattern separation parallel in O(log2 n) steps for n neurons and sparse coding.

Action Potentials↗
PubMed2004

Coexistence of memory patterns and mixed states in a sparsely encoded associative memory model storing ultrametric patterns.

Analyzing the coexistence of memory patterns and mixed states gives important information for constructing a model for the face responsive neurons of the monkey inferior-temporal cortex. We analyzed whether the memory patterns coexist with mixed states when the sparse coding scheme is used for the associative memory model storing ultrametric patterns. For memory patterns and mixed states to coexist, there must be sufficient capacity for storing them and their threshold values must be the same. We determined that the storage capacities for all mixed states composed of correlated memory patterns diverge as 1/| f log f| (where f is the firing rate) even when the correlation of the memory patterns is infinitesimally small. We also determined that the memory patterns and the mixed states can become the equilibrium state of the model in the same threshold value. These results mean that they can coexist in this model. These findings should contribute to research on face responsive neurons in the monkey inferior-temporal cortex.

Action Potentials↗
PubMed1998

A model of cortical associative memory based on a horizontal network of connected columns.

An attractor network model of cortical associative memory functions has been constructed and simulated. By replacing the single cell as the functional unit by multiple cells in cortical columns connected by long-range fibers, the model is improved in terms of correspondence with cortical connectivity. The connectivity is improved, since the original dense and symmetric connectivity of a standard recurrent network becomes sparse and asymmetric at the cell-to-cell level. Our simulations show that this kind of network, with model neurons of the Hodgkin-Huxley type arranged in columns, can operate as an associative memory in much the same way as previous models having simpler connectivity. The network shows attractor-like behaviour and performs the standard assembly operations despite differences in the dynamics introduced by the more detailed cell model and network structure. Furthermore, the model has become sufficiently detailed to allow evaluation against electrophysiological and anatomical observations. For instance, cell activities comply with experimental findings and reaction times are within biological and psychological ranges. By introducing a scaling model we demonstrate that a network approaching experimentally reported neuron numbers and synaptic distributions also could work like the model studied here.

Action Potentials↗
PubMed1992

Development of self-recognition in chimpanzees (Pan troglodytes).

Chimpanzees (Pan troglodytes) demonstrate the ability to recognize themselves in mirrors, yet investigations of the development of self-recognition in chimpanzees are sparse. Twelve young chimpanzees, grouped by age, were given mirror exposure and tested for self-recognition and contingent movement. All 6 juveniles, 4 and 5 years old, exhibited mirror-guided, mark-directed behavior and clear evidence of self-recognition. In contrast, among the infants, only the oldest group of 2 1/2-year-olds exhibited clear evidence of self-recognition. All chimpanzees exhibited both self-directed behaviors and contingent movements. These results suggest that self-recognition occurs at a slightly older age in chimpanzees than in human infants. In humans, self-recognition is linked with other cognitive abilities. The results conform to the general pattern that great apes exhibit many cognitive skills comparable to those of 2-year-old humans.

Affect↗
PubMed2005

Transient information flow in a network of excitatory and inhibitory model neurons: role of noise and signal autocorrelation.

We investigate the performance of sparsely-connected networks of integrate-and-fire neurons for ultra-short term information processing. We exploit the fact that the population activity of networks with balanced excitation and inhibition can switch from an oscillatory firing regime to a state of asynchronous irregular firing or quiescence depending on the rate of external background spikes. We find that in terms of information buffering the network performs best for a moderate, non-zero, amount of noise. Analogous to the phenomenon of stochastic resonance the performance decreases for higher and lower noise levels. The optimal amount of noise corresponds to the transition zone between a quiescent state and a regime of stochastic dynamics. This provides a potential explanation of the role of non-oscillatory population activity in a simplified model of cortical micro-circuits.

Action Potentials↗
PubMed1990

Similarity neighborhoods of spoken two-syllable words: retroactive effects on multiple activation.

This research examines the recognition of two-syllable spoken words and the means by which the auditory word recognition process deals with ambiguous stimulus information. The experiments reported here investigate the influence of individual syllables within two-syllable words on the recognition of each other. Specifically, perceptual identification of two-syllable words comprised of two monosyllabic words (spondees) was examined. Individual syllables within a spondee were characterized as either "easy" or "hard" depending on the syllable's neighborhood characteristics; an easy syllable was defined as a high-frequency word in a sparse neighborhood of low-frequency words, and a hard syllable as a low-frequency word in a high-density, high-frequency neighborhood. In Experiment 1, stimuli were created by splicing together recordings of the component syllables of the spondee, thus equating for syllable stress. Additional experiments tested the perceptual identification of naturally produced spondees, spliced nonwords, and monosyllables alone. Neighborhood structure had a strong effect on identification in all experiments. In addition, identification performance for spondees with a hard-easy syllable pattern was higher than for spondees with an easy-hard syllable pattern, indicating a primarily retroactive pattern of influence in spoken word recognition. Results strongly suggest that word recognition involves multiple activation and delayed commitment, thus ensuring accurate and efficient recognition.

Adult↗
PubMed2005

Crowded and sparse domains in object recognition: consequences for categorization and naming.

Some models of object recognition propose that items from structurally crowded categories (e.g., living things) permit faster access to superordinate semantic information than structurally dissimilar categories (e.g., nonliving things), but slower access to individual object information when naming items. We present four experiments that utilize the same matched stimuli: two examine superordinate categorization and two examine picture naming. Experiments 1 and 2 required participants to sort pictures into their appropriate superordinate categories and both revealed faster categorization for living than nonliving things. Nonetheless, the living thing superiority disappeared when the atypical categories of body parts and musical instruments were excluded. Experiment 3 examined naming latency and found no difference between living and nonliving things. This finding was replicated in Experiment 4 where the same items were presented in different formats (e.g., color and line-drawn versions). Taken as a whole, these experiments show that the ease with which people categorize items maps strongly onto the ease with which they name them.

Adult↗
PubMed1983

How many trees does it take to make a forest?

In order to study the relative perceptual availability of global and local features in very sparse patterns, subjects were asked to make 'same'/'different' judgments on pairs of geometrical figures and the times needed to detect global and local differences were compared. With triangular patterns a global precedence was found which could be attributed to size differences. With rectangular patterns global precedence was larger, not accounted for by size differences, and indifferent both to the number of elements and to their spacing. Thus it was demonstrated that global precedence may hold for patterns with as few as four elements. Patterns with smooth edges could be compared much more quickly than patterns with serrated eges. It is proposed that configurational properties of some of the patterns interfered with the encoding of their global structures or with comparing them. It is argued that the results support a principle of global addressability which postulates that visual schemata are mainly addressed through their global constituents.

Discrimination Learning↗
PubMed2006

Minimal access spinal surgery (MASS) in treating thoracic spine metastasis.

STUDY DESIGN: A retrospective study was conducted. OBJECTIVE: This study aims to analyze the feasibility and efficacy of using minimal access spinal surgery (MASS) for managing thoracic spine metastasis. SUMMARY OF BACKGROUND DATA: Literature regarding minimally invasive surgical treatment for thoracic spine metastasis is sparse. In the past decade, the role of minimally invasive or endoscopic technique in managing metastatic thoracic disease has evolved. METHODS: From February 1997 to March 2003, 46 patients with spine metastases, from T3-T12, were enrolled in this study. There were 29 patients undergoing MASS. Seventeen patients received standard thoracotomy (ST) in the early study period served as the control group. The indications for MASS include intractable back pain and/or neurologic deficits or neurologic deterioration during or after radiotherapy. Inclusion criteria for this study included tumor limited to one or two vertebral segments. RESULTS: In the MASS and ST groups, no patient died as a result of an immediate intraoperative event. The mean operative blood loss was 1,110 versus 1,162 mL (P = 0.63), and the mean operative length was 179 versus 180 minutes (P = 0.54). Complication rates and 1-year, 2-year, and overall survival rates were comparable and the mean grade of neurologic recovery was 1.2 on the Frankel scale in both groups. Only 6.9% of MASS patients required a 2-day postoperative ICU stay compared with 88% of ST patients (P < 0.0001). CONCLUSIONS: The MASS technique is safe and effective and has proved to be an excellent alternative in managing thoracic spine metastasis. Surgeons may use progressively smaller incisions (5-6 cm in length) for the procedure. The learning curve for performing MASS procedures was not steep.

Adult↗
PubMedDate not supplied

Animal models of periadolescent substance abuse.

Use of addictive substances by human juveniles and adolescents is common, including use to intoxication and progression from one drug to other drugs. Until quite recently, animal studies have not addressed the periadolescent period as a time of special vulnerability to substance abuse. For ethanol (EtOH), the most studied drug in periadolescent animals, it has become clear that effects of alcohol are similar in some ways, but different in others, compared to the effects seen in adult animals. Sparse data suggest that this conclusion may apply to other drugs as well. Recent work in rats indicates that periadolescent substance use may disrupt normal pubertal development, and may induce stronger effects on systems subserving plasticity and cognition than in adults. Animal data also indicate that some drugs may produce altered subsequent sensitivity to the same or a different drug, changes in adult cognitive capabilities, and even CNS damage. It is now clear that there can be no presumption that all studies of abusable substances carried out in adult animals will generalize readily to periadolescents. Some data suggest that continuing developmental changes in receptor expression may underlie age-related changes in drug effects. However, the biological characteristics of periadolescence which predispose toward consumption to intoxication, and the mechanisms underlying drug progression and persisting drug effects, still remain to be well defined.

Adolescent↗
PubMed1994

Information processing within the motor cortex. I. Responses of morphologically identified motor cortical cells to stimulation of the somatosensory cortex.

Inputs from the somatosensory cortex to the motor cortex have been proposed to function in learning of motor skills. In an attempt to analyze how these somatosensory inputs were processed in the motor cortex, neurons in the superficial layer of the cat motor cortex were classified into three groups on the basis of synaptic responses elicited by intracortical microstimulation (ICMS) of area 2. ICMS was delivered through seven electrodes implanted in area 2. When ICMS through one of the seven sites produced a response that was greater than 50% of the response produced by stimulating the seven sites at a time, the site was called a "dominant" site. Type I cells were those that had a dominant stimulation site and showed a constant response latency when examined by a double shock test. Type II cells were those that had a dominant site but displayed a variable latency. Type III cells had no dominant site and showed a variable latency. Latency of type I responses was 1.2-2.6 milliseconds, which was much shorter than that of type II and type III responses. Seventy-nine neurons in layers II/III of the motor cortex, which responded to ICMS in area 2, were stained by intracellular injection of biocytin. From the presence of an apical dendrite and rich spines on the dendrites, 23 type I, 21 type II, and 15 type III cells were classified as pyramidal cells. Type II pyramidal cells were located more superficially than type I and type III pyramidal cells. On the basis of the absence or sparseness of dendritic spines, three type I and four type II cells in layers II/III were classified as nonpyramidal cells. These cells consisted of five small multipolar cells in layer II and a large multipolar cell and a small bitufted cell in layer III. The remaining 11 cells were not classified because of insufficient staining. Since type I and type II cells are considered to represent monosynaptic and polysynaptic responses to stimulation of area 2, respectively, information flow from type I cells to more superficially located type II cells is presumed in layers II/III of the motor cortex. Type III responses suggest the presence of a convergent flow of impulses inside of and/or between areas 2 and 4.

Animals↗
PubMedDate not supplied

Perception of kinetic illusory contours by two-month-old infants.

Perception of kinetic illusory contours by 2-month-old infants was explored with sparse random-dot displays depicting an illusory shape against a background. In Experiment 1, 24 infants were habituated to a shape specified by accretion and deletion of background texture and relative motion, and exhibited a novelty preference when presented with luminance-defined familiar and novel shapes. Subsequent experiments explored kinetic cues in isolation. In Experiment 2 (n = 24), relative motion information was removed, leaving accretion and deletion of texture and luminance cues, and in Experiment 3 (n = 24), only relative motion information was available. In both these experiments the novelty preference obtained in Experiment 1 was replicated. Results from a control condition (n = 12) mitigated against the likelihood of an inherent preference for either of the test shapes. These findings reveal an early capacity to perceive shape solely from kinetic information, and suggest a mechanism geared toward spatiotemporal boundary formation that is functional shortly after birth. Theories of development of edge and motion discrimination are discussed.

Adult↗