Noise-driven neuroplasticity in self-organizing feature maps: a neurocomputational model of phantom limbs

The term "phantom limb" denotes the sensation that an extremity is present although it has been lost. A number of clinical features and recent findings of cortical map plasticity after destruction of afferent pathways (deafferentation) suggest that phantom limbs are caused by large-scale cortical reorganization processes. However, in paraplegics, who also suffer from cortical deafferentation, phantom sensations rarely develop, and if they do, they are weak, lacking in detail, and delayed, occurring after months. This has been taken to suggest a non-cortical genesis of phantom limbs. This article proposes a biologically plausible minimal neural network model to solve this apparent puzzle. Deafferentation was simulated in trained self-organizing feature maps. Reorganization was found to be directed by input noise. According to the model, the production of input noise by the deafferented primary sensory neuron promotes cortical reorganization in amputees. No such noise is generated or conducted to the cortex in paraplegics.     

Atypical form of Alzheimer's disease with prominent posterior cortical atrophy: a review of lesion distribution and circuit disconnection in cortical visual pathways

In recent years, the existence of visual variants of Alzheimer's disease characterized by atypical clinical presentation at onset has been increasingly recognized. In many of these cases post-mortem neuropathological assessment revealed that correlations could be established between clinical symptoms and the distribution of neurodegenerative lesions. We have analyzed a series of Alzheimer's disease patients presenting with prominent visual symptomatology as a cardinal sign of the disease. In these cases, a shift in the distribution of pathological lesions was observed such that the primary visual areas and certain visual association areas within the occipito-parieto-temporal junction and posterior cingulate cortex had very high densities of lesions, whereas the prefrontal cortex had fewer lesions than usually observed in Alzheimer's disease. Previous quantitative analyses have demonstrated that in Alzheimer's disease, primary sensory and motor cortical areas are less damaged than the multimodal association areas of the frontal and temporal lobes, as indicated by the laminar and regional distribution patterns of neurofibrillary tangles and senile plaques. The distribution of pathological lesions in the cerebral cortex of Alzheimer's disease cases with visual symptomatology revealed that specific visual association pathways were disrupted, whereas these particular connections are likely to be affected to a less severe degree in the more common form of Alzheimer's disease. These data suggest that in some cases with visual variants of Alzheimer's disease, the neurological symptomatology may be related to the loss of certain components of the cortical visual pathways, as reflected by the particular distribution of the neuropathological markers of the disease.     

Calvarial eosinophilic granuloma: diagnostic models and image feature selection with a neural network

We used thoracic SPECT to study the 99mTc-tetrofosmin (TF) uptake in patients with non-small-cell-lung-carcinoma (NSCLC). The results were compared with the percentage of P-glycoprotein (Pgp) found in flow cytometric analysis (FC) of samples of surgically-resected tumor tissue. MATERIAL AND METHODS: A total of 21 patients with NSCLC were studied by means 99mTC-TF and thoracic SPECT. Image analysis included the determination of the TF uptake rate in the lung mass with respect to that of healthy tissue of the contralateral lung. These rates were compared with the percentage of Pgp expression according to FC. FC analysis was also carried out in 16 samples of healthy lung tissue obtained from the patients. RESULTS: In healthy lung tissue, the mean Pgp expression according to FC was 4.58 +/- 1.87%. The cutoff value used to differentiate between Pgp positive and Pgp negative tumors was considered to be the mean plus two standard deviations (8.32). The Pgp-positive tumors (> 8.32%) presented significantly lower uptake levels (1.28 +/- 0.39) than the Pgp-negative lesions (1.66 +/- 0.33) (p = 0.029). CONCLUSIONS: There is a inverse correlation between the Pgp expression as determined by FC analysis and 99mTc-TF in NSCLC. Thus, this radiopharmaceutical provides rapid and non-invasive information on Pgp expression in these lesions.     

Brief report: how far can people with autism go in developing a theory of mind?

Although T cells arise in the thymus, migration of mature postthymic T cells back to the thymus is very limited in adult mice and is restricted to activated cells. In neonates, by contrast, we present evidence that circulating CD4+ and CD8+ T cells with a naive/resting phenotype readily enter the thymus after intravenous injection and remain there for prolonged periods. The migration of resting T cells to the neonatal thymus is largely limited to an unusual subset of cells which lacks expression of the lymph node homing receptor, leukocyte-endothelial cell adhesion molecule 1 (LECAM-1) (MEL-14). Migration of mature T cells to the thymus in neonates may be important for self-tolerance induction.     

Integrating neural networks into decision-making and motivational theory: Rethinking VIE theory.

[Correction Notice: An erratum for this article was reported in Vol 44(3) of Canadian Psychology/Psychologie Canadienne (see record 2007-16858-001). The paper by Lord, Henges and Godfrey, referred to in some of the commentaries (this issue), was accepted as part of the Special Section on psychology without boundaries. However, it was inadvertently published in a previous issue. The full reference is: Lord, R. G., Hanges, P. J., & Godfrey, E. G. (2003). Integrating neural networks into decision-making and motivational theory: Rethinking VIE theory. Canadian Psychology, 44 (1), 21-38.] Uses a reformulation of V. H. Vroom's (1964) VIE (Valence-Instrumentality-Expectancy) theory to illustrate the potential value of neuropsychologically based models of cognitive processes. Vroom's theory posits that people's decisions are determined by their affective reactions to certain outcomes (valences), beliefs about the relationship between actions and outcomes (expectancies), and perceptions of the association between primary and secondary outcomes (instrumentalities). One of the major criticisms of this type of theory is that the computations it requires are unrealistically time-consuming and often exceed working memory capacity. In this paper, the authors maintain that if an individual has extensive experience with a problem situation, he or she can process decisions about that situation using neural networks that operate implicitly so that cognitive resources are not exhausted by simple computations; instead, the computations are performed implicitly by neural networks. By thinking about VIE from a neural network standpoint, at least one of its problems is eliminated, and several new insights into decision-making are provided. The authors use simulation methodology to show that such a model is both viable and can reflect the effects of current goals on choice processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Registration of neural maps through value-dependent learning: modeling the alignment of auditory and visual maps in the barn owl's optic tectum

In the optic tectum (OT) of the barn owl, visual and auditory maps of space are found in close alignment with each other. Experiments in which such alignment has been disrupted have shown a considerable degree of plasticity in the auditory map. The external nucleus of the inferior colliculus (ICx), an auditory center that projects massively to the tectum, is the main site of plasticity; however, it is unclear by what mechanisms the alignment between the auditory map in the ICx and the visual map in the tectum is established and maintained. In this paper, we propose that such map alignment occurs through a process of value-dependent learning. According to this paradigm, value systems, identifiable with neuromodulatory systems having diffuse projections, respond to innate or acquired salient cues and modulate changes in synaptic efficacy in many brain regions. To test the self-consistency of this proposal, we have developed a computer model of the principal neural structures involved in the process of auditory localization in the barn owl. This is complemented by simulations of aspects of the barn owl phenotype and of the experimental environment. In the model, a value system is activated whenever the owl carries out a foveation toward an auditory stimulus. A term representing the diffuse release of a neuromodulator interacts with local pre- and postsynaptic events to determine synaptic changes in the ICx. Through large-scale simulations, we have replicated a number of experimental observations on the development of spatial alignment between the auditory and visual maps during normal visual experience, after the retinal image is shifted through prismatic goggles, and after the reestablishment of normal visual input. The results suggest that value-dependent learning is sufficient to account for the registration of auditory and visual maps of space in the OT of the barn owl, and they lead to a number of experimental predictions.     

Visual feature integration theory: Past, present, and future.

Visual feature integration theory was one of the most influential theories of visual information processing in the last quarter of the 20th century. This article provides an exposition of the theory and a review of the associated data. In the past much emphasis has been placed on how the theory explains performance in various visual search tasks. The relevant literature is discussed and alternative accounts are described. Amendments to the theory are also set out. Many other issues concerning internal processes and representations implicated by the theory are reviewed. The article closes with a synopsis of what has been learned from consideration of the theory, and it is concluded that some of the issues may remain intractable unless appropriate neuroscientific investigations are carried out. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extraversion and performance: A test of the theory of cortical inhibition.

Hypothesized that extraversion scores should correlate with scores on performance tasks purported to depend on cortical inhibition. Data from 104 undergraduates who performed spatial and internal inhibition tasks did not reveal any significant correlations between extraversion (Maudsley Personality Inventory) and performance measures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A neural theory of binocular rivalry.

When the two eyes view discrepant monocular stimuli, stable single vision gives way to alternating periods of monocular dominance; this is the well-known but little understood phenomenon of binocular rivalry. This article develops a neural theory of binocular rivalry that treats the phenomenon as the default outcome when binocular correspondence cannot be established. The theory posits the existence of monocular and binocular neurons arrayed within a functional processing module, with monocular neurons playing a crucial role in signaling the stimulus conditions instigating rivalry and generating inhibitory signals to implement suppression. Suppression is conceived as a local process happening in parallel over the entire cortical representation of the binocular visual field. The strength of inhibition causing suppression is related to the size of the pool of monocular neurons innervated by the suppressed eye, and the duration of a suppression phase is attributed to the strength of excitation generated by the suppressed stimulus. The theory is compared with three other contemporary theories of binocular rivalry. The article closes with a discussion of some of the unresolved problems related to the theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial cognitive maps in animals: New hypotheses on their structure and neural mechanisms.

Provides a hierarchical model of animal spatial cognitive maps. Such maps include both topological information, which affords loose, yet operational, representations of the connectivity of space and its overall arrangement, and metric information, which provides information about angles and distances. The model holds that maps can be initially described as a set of location-dependent reference frameworks providing directional information about other locations. The addition of an overall directional reference allows for the buildup of more complete (allocentric) representations. A survey of recent neurobiological data provides some hints about the brain structures involved in these processes and suggests that the hippocampal formation and the posterior parietal cortex would act differently by handling topological and metric information, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inadequate management of blood pressure in a hypertensive population

BACKGROUND: Many patients with hypertension have inadequate control of their blood pressure. Improving the treatment of hypertension requires an understanding of the ways in which physicians manage this condition and a means of assessing the efficacy of this care. METHODS: We examined the care of 800 hypertensive men at five Department of Veterans Affairs sites in New England over a two-year period. Their mean (+/-SD) age was 65.5+/-9.1 years, and the average duration of hypertension was 12.6+/-5.3 years. We used recursive partitioning to assess the probability that antihypertensive therapy would be increased at a given clinic visit using several variables. We then used these predictions to define the intensity of treatment for each patient during the study period, and we examined the associations between the intensity of treatment and the degree of control of blood pressure. RESULTS: Approximately 40 percent of the patients had a blood pressure of > or =160/90 mm Hg despite an average of more than six hypertension-related visits per year. Increases in therapy occurred during 6.7 percent of visits. Characteristics associated with an increase in antihypertensive therapy included increased levels of both systolic and diastolic blood pressure at that visit (but not previous visits), a previous change in therapy, the presence of coronary artery disease, and a scheduled visit. Patients who had more intensive therapy had significantly (P<0.01) better control of blood pressure. During the two-year period, systolic blood pressure declined by 6.3 mm Hg among patients with the most intensive treatment, but increased by 4.8 mm Hg among the patients with the least intensive treatment. CONCLUSIONS: In a selected population of older men, blood pressure was poorly controlled in many. Those who received more intensive medical therapy had better control. Many physicians are not aggressive enough in their approach to hypertension.     

What is needed for a theory of mobility: Direct perceptions and cognitive maps—lessons from the blind.

Proposes a theory of mobility, using nonvisual stimuli and a cognitive control process to augment J. J. Gibson's (1979; see also PA, Vol 33:9697) explanations of visual guidance. This proposed theory of mobility explains the nonvisual processes that underlie travel by both blind and sighted persons. The author stresses: (1) the importance of perceptual or cognitive representations of the environment in controlling mobility; and (2) how the regularities of the human-made environment influence the nature of travel activities and spatial cognition. Mobility can be directed by visual control stimuli in the ambient optic array; by nonvisual control stimuli; and by processes of spatial learning, including stimulus–response rote learning, motor plans, schemas, and cognitive maps. The selection of processes and strategies depends on the availability of particular information or on task demands. Attentional processes select stimuli for locomotor control within any particular modality and select between perceptual and cognitive processes. (109 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of developmental regression in autism and the broader phenotype: A neural network modeling approach.

Loss of previously established behaviors in early childhood constitutes a markedly atypical developmental trajectory. It is found almost uniquely in autism and its cause is currently unknown (Baird et al., 2008). We present an artificial neural network model of developmental regression, exploring the hypothesis that regression is caused by overaggressive synaptic pruning and identifying the mechanisms involved. We used a novel population-modeling technique to investigate developmental deficits, in which both neurocomputational parameters and the learning environment were varied across a large number of simulated individuals. Regression was generated by the atypical setting of a single pruning-related parameter. We observed a probabilistic relationship between the atypical pruning parameter and the presence of regression, as well as variability in the onset, severity, behavioral specificity, and recovery from regression. Other neurocomputational parameters that varied across the population modulated the risk that an individual would show regression. We considered a further hypothesis that behavioral regression may index an underlying anomaly characterizing the broader autism phenotype. If this is the case, we show how the model also accounts for several additional findings: shared gene variants between autism and language impairment (Vernes et al., 2008); larger brain size in autism but only in early development (Redcay & Courchesne, 2005); and the possibility of quasi-autism, caused by extreme environmental deprivation (Rutter et al., 1999). We make a novel prediction that the earliest developmental symptoms in the emergence of autism should be sensory and motor rather than social and review empirical data offering preliminary support for this prediction. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A formal theory of feature binding in object perception.

Visual objects are perceived correctly only if their features are identified and then bound together. Illusory conjunctions result when feature identification is correct but an error occurs during feature binding. A new model is proposed that assumes feature binding errors occur because of uncertainty about the location of visual features. This model accounted for data from 2 new experiments better than a model derived from A. M. Treisman and H. Schmidt's (see record 1982-07512-001) feature integration theory. The traditional method for detecting the occurrence of true illusory conjunctions is shown to be fundamentally flawed. A reexamination of 2 previous studies provided new insights into the role of attention and location information in object perception and a reinterpretation of the deficits in patients who exhibit attentional disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The self-concept revisited: Or a theory of a theory.

Attempts to integrate phenomenological theories of the self-concept into a broader framework compatible with an objective approach. The phenomenological theories that identify the self-concept as the nucleus of the personality with directive and integrative properties become intelligible when the self-concept is redefined as a "self-theory" that the individual has unwittingly constructed about himself as an experiencing, functioning individual. The self-theory supplements a "world theory," which encompasses the remaining significant aspects of experience. An individual's self-theory consists of a hierarchical arrangement of major and minor postulates. The postulates can be operationally identified by the cognitions implicit in the individual's emotional responses to events. The individual develops his self-theory to assist in the maintenance of a favorable pleasure-pain balance, assimilate the data of experience, and maintain self-esteem. A failure in any of these functions produces mounting stress, and ultimately collapse of the self-theory, which can be adaptive in providing an opportunity for drastic reorganization. (22 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A neural systems theory of schizophrenia and tardive dyskinesia

Some systems ideas applied to individual persons are used to try to explain symptoms of schizophrenia and a syndrome of uncontrolled fragments of movement which sometimes occurs as a side effect of chronic, antipsychotic drug therapy. The behavior of normal organisms may be conceptualized in three echelons of control, with each successively higher echelon organizing, by selective disinhibition, semiautonomous, spontaneous fragments of activity which comprise the next lower echelon. It is hypothesized that schizophrenia involves a deficiency of inhibition by the frontal cortex, first echelon, on the corpus striatum, second echelon. This results first in insufficiently integrated fragments of behavior, and second in premature associative linkages among active elements. First echelon control develops as a normal person matures and gradually loses some of the playful activities of childhood. It is hypothesized that by disrupting certain aspects of activity in the corpus striatum, neuroleptic drugs reduce schizophrenic symptoms but also reduce the capacity of the second echelon to inhibit and integrate the smaller behavioral fragments wired into lower parts of the brain, third echelon. This results in uncontrolled movements. Though many researchers already favor the hypothesis that neuroleptic drugs act on the corpus striatum, the broader theory presented here is new and depends in large part on general living systems considerations. Emphasis is on conceptual decomposition of the integrated behavior of a whole organism into less complex subsystems. Individually, these have neither too much nor too little complexity to yield a plausible model. Some experimental predictions and predictions about possible therapies are made from the theory.