Toward an interpretation of dynamic neural activity in terms of chaotic dynamical systems

Using the concepts of chaotic dynamical systems, we present an interpretation of dynamic neural activity found in cortical and subcortical areas. The discovery of chaotic itinerancy in high-dimensional dynamical systems with and without a noise term has motivated a new interpretation of this dynamic neural activity, cast in terms of the high-dimensional transitory dynamics among "exotic" attractors. This interpretation is quite different from the conventional one, cast in terms of simple behavior on low-dimensional attractors. Skarda and Freeman (1987) presented evidence in support of the conclusion that animals cannot memorize odor without chaotic activity of neuron populations. Following their work, we study the role of chaotic dynamics in biological information processing, perception, and memory. We propose a new coding scheme of information in chaos-driven contracting systems we refer to as Cantor coding. Since these systems are found in the hippocampal formation and also in the olfactory system, the proposed coding scheme should be of biological significance. Based on these intensive studies, a hypothesis regarding the formation of episodic memory is given.     

LF-interpretability and language development: a study of verbal and nominal features in Greek normally developing and SLI children

This paper includes (i) a comparison of the developmental pattern of certain morphosyntactic features in normally developing (ND) Greek children with similar data from a group of children with specific language impairment and (ii) a new analysis of the differences found. The analysis is based on a minimalist notion of LF interpretability. Depending on the feature-specification of lexical items (i.e., [+/- interpretable] at LF), a different route of development follows. In addition, phonological salience of both interpretable and noninterpretable features is argued to play an important role in an account of crosslinguistic differences in both normal and exceptional development.     

Representation of visuotactile space in the split brain

Recent neurophysiological research in the monkey has revealed bimodal neuronal cells with both tactile receptive fields on the hand and visual receptive fields that follow the hands as they move, suggesting the existence of a bimodal map of visuotactile space. Using a cross-modal congruency task, we examined the representation of visuotactile space in normal people and in a split-brain patient (J.W.) as the right arm assumed different postures. The results showed that the congruency effects from distracting lights followed the hand around in space in normal people, but failed to do so in the split-brain patient when the hand crossed the midline. This suggests that cross-cortical connections are required to remap visual space to the current hand position when the hand crosses the midline.     

Prevalence,and intellectual outcome of unilateral focal cortical brain damage as a function of age,sex and aetiology

Neurologists and neuropsychologists are aware that aging men are more at risk than women for brain damage, principally because of the well known male-predominant risk for cardiovascular disease and related cerebrovascular accidents. However, a disproportion in prevalence of brain damage between the sexes in childhood may be less suspected. Furthermore, sex-specific risk for other aetiologies of brain damage may be little known, whether in the pediatric or adult populations. Proposals of a sex difference in cognitive recovery from brain damage have also been controversial. Six hundred and thirty five "consecutive" cases with cortical focal lesions including cases of all ages and both sexes were reviewed. Aetiology of the lesion was determined for each case as was postlesion IQ. Risk was highly male prevalent in all age groups, with a predominance of cardiovascular aetiology explaining much of the adult male prevalence. However, several other aetiological categories were significantly male prevalent in juveniles (mitotic, traumatic, dysplasic) and adults (mitotic, traumatic). There was no sex difference in outcome (i.e., postlesion IQ) of these cortical brain lesions for the cohort as a whole, after statistical removal of the influence of lesion extent, aetiology and presence of epilepsy. Mechanisms potentially responsible for sex differences in prevalence, aetiology of brain damage, and recovery, are reviewed and discussed.     

Excessive reassurance seeking: delineating a risk factor involved in the development of depressive symptoms

Six studies investigated (a) the construct validity of reassurance seeking and (b) reassurance seeking as a specific vulnerability factor for depressive symptoms. Studies 1 and 2 demonstrated that reassurance seeking is a reasonably cohesive, replicable, and valid construct, discernible from related interpersonal variables. Study 3 demonstrated that reassurance seeking displayed diagnostic specificity to depression, whereas other interpersonal variables did not, in a sample of clinically diagnosed participants. Study 4 prospectively assessed a group of initially symptom-free participants, and showed that those who developed future depressive symptoms (as compared with those who remained symptom-free) obtained elevated reassurance-seeking scores at baseline, when all participants were symptom-free, but did not obtain elevated scores on other interpersonal variables. Studies 5 and 6 indicate that reassurance seeking predicts future depressive reactions to stress. Taken together, the six studies support the construct validity of reassurance seeking, as well as its potential role as a specific vulnerability factor for depression.     

Target detection in scientific visualization

Three experiments were conducted to test participants' ability to detect targets in colored spatial displays using 7-level bipolar scales. Experiment 1 assessed the ability of participants to detect high or low targets using 12 scales whose poles either were directly opposed in color space or had a primary and an intermediate hue at each pole. Experiment 2 used 8 scales whose arms were orthogonal in color space. Experiment 3 examined the simultaneous detection of high and low targets. Although there are notable exceptions, scales that are close to or above the horizontal (red-green) axis in color space perform best. Of the scales with orthogonal arms, those that are oriented downward, toward the blues, in color space are least satisfactory. Scales that are asymmetrically effective are common, and applications requiring good detectability at both extremes must take this into account. The results are discussed in the context of the evolution of trichromatic color vision.     

Bertrand Russell in His Nineties: Aging and the Problem of Biography

Bertrand Russell, one of the twentieth century's leading philosophers, lived to be ninety-eight, spending his last decade as a vigorous and often unpopular political activist. His generally sympathetic biographers tend to view this last decade through the prism of senility, but the only justification for this judgment would appear to be the objective fact of Russell's age. Almost identical behaviors from his younger years are never attributed to mental shortcomings. The treatment of Russell suggests that biographers are susceptible to powerful, distorting, and fictive predispositions as they shape their subjects' later years.     

Self-injurious behavior: gene-brain-behavior relationships

This paper summarizes a conference held at the National Institute of Child Health and Human Development on December 6-7, 1999, on self-injurious behavior [SIB] in developmental disabilities. Twenty-six of the top researchers in the U.S. from this field representing 13 different disciplines discussed environmental mechanisms, epidemiology, behavioral and pharmacological intervention strategies, neurochemical substrates, genetic syndromes in which SIB is a prominent behavioral phenotype, neurobiological and neurodevelopmental factors affecting SIB in humans as well as a variety of animal models of SIB. Findings over the last decade, especially new discoveries since 1995, were emphasized. SIB is a rapidly growing area of scientific interest to both basic and applied researchers. In many respects it is a model for the study of gene-brain-behavior relationships in developmental disabilities.     

Context-specificity of relapse: effects of therapist and environmental context on return of fear.

Context-specificity of fear extinction was tested among 65 participants who were fearful of spiders by manipulating the contexts used for exposure treatment and two-week follow-up assessment. Context was defined by both meaningful (presence of a particular therapist) and incidental (room location and furnishings) environmental cues. Distinct phobic stimuli were used to examine interactions of context with stimulus. Physiological, behavioral and verbal indices of fear were measured. Results provided modest support for context-specific return of fear. With one stimulus, participants assessed in a non-treatment context at follow-up exhibited greater returns in heart rate levels. In addition, three of four participants who could not touch the stimulus at follow-up had been tested in a non-treatment context. Future investigations may benefit from greater distinctions between contexts or manipulation of contextual features more directly relevant to fear. Finally, post hoc analyses identified high trait anxiety, slow treatment response, recovery of phobic cognitions and long duration/high intensity phobic encounters post-treatment as significant predictors of increased return of fear.     

Psychopathological correlates of self-reported behavioural inhibition in normal children.

The present study examined the relationship between self-reported behavioural inhibition and psychopathological symptoms in a sample of 152 children aged 12-14 years. Children were provided with a definition of behavioural inhibition and then asked to classify themselves as low, middle or high on behavioural inhibition. Furthermore, children completed questionnaires of worry, depression and anxiety symptoms. Results showed that children who endorsed the high behavioural inhibition category had elevated levels of anxiety, worry and depression compared to children who endorsed the low or middle behavioural inhibition categories. Moreover, children high on behavioural inhibition more frequently reported anxiety disorders symptoms in the subclinical range. These findings fit well with those of previous studies on behavioural inhibition.