A few remarks on attention and magnocellular deficits in schizophrenia

In connection with schizophrenia, it has been proposed that the magnocellular system is specifically linked to the guiding of covert visual attention. The argument is that the magnocellular pathway provides input to the dorsal cortical stream which then projects back to area V1. We review problems with this model. (1) It requires that responses in the magnocellular system have a lead time over responses in the parvocellular system. However, measurements indicate that the actual response time difference between the two systems is small or negligible when entering the visual cortex. (2) Attention can be modified by stimuli that do not activate the magnocellular system. And, (3) lesions to area MT in the dorsal stream impair smooth pursuit eye movements, but not saccadic eye movements which are associated with shifts in attention. For these reasons, it is difficult to link attention defects in schizophrenia to potential magnocellular deficits.     

A few remarks on relating reaction time to magnocellular activity

Studies have found dyslexic readers to have longer reaction times than nondyslexic readers. These results have been discussed relative to the hypothesis that dyslexia is caused by a magnocellular deficit. We here point out that attempts to link reaction times in dyslexic readers to magnocellular sensitivity face at least two serious problems: (a) The reaction time differences between dyslexics and controls appear too large to be attributable to deficits in the magnocellular system; (b) there is evidence to suggest that in the case of stimuli with contrast above about 10% behavioral reaction times may reflect parvocellular rather than magnocellular activity.     

A developmental perspective on psychotherapy and psychoanalysis

Some of the most important issues in dynamic psychiatry involve the mechanisms of action of and the distinctions between psychotherapy and psychoanalysis. Recent advances in developmental psychology and in clinical practice and theory provide new insights into these long-standing controversies.     

The advantage in being magnocellular: a few more remarks on attention and the magnocellular system

We have recently proposed a model of visual processing in which object recognition through the ventral stream into inferotemporal cortex is facilitated by an initial rapid feedforward sweep through the dorsal stream activating parietal and frontal regions prior to subsequent feedback to primary visual cortex (V1). Modulation of inferotemporal cortex also requires feedback from frontal regions, and horizontal connections from the dorsal stream. Aspects of this model, however, have been called into question-in particular the timing advantage of magnocellular over parvocellular arrivals in V1 (the 'magnocellular advantage'), the link between attention and the magnocellular system, and also the role of MT in smooth pursuit and saccadic eye movements. These criticisms are each rebutted in detail here, and the basis for a model derived from the magnocellular advantage is reaffirmed.     

Further thoughts on dualism, science, and the use of medication in psychoanalysis.

In response to Deborah Cabaniss's article, "Beyond Dualism: Psychoanalysis and Medication in the 21st Century," the author further considers the differences between the aims of symptom reduction and psychic integration, the concept of mind-body dualism, and the nature of scientific inquiry as they pertain to the use of medication in psychoanalytic therapies. He warns against the collapsing of concepts, aided by a misapplication of science, with respect to how we listen to, organize, and respond to clinical material. He argues that only when such scrutiny occurs can the important and challenging questions pertaining to the use of medication in psychoanalytic therapies be meaningfully considered.     

Anxiety, arousal, and autonomic habituation.

The interaction of anxiety and autonomic activation as a factor in the development and persistency of pathological anxiety was investigated with the aid of self-rating procedures and a habituation experiment. The state of activation was varied systematically in 40 normal subjects by various experimental conditions and by the administration of a tranquilizer. The degree of anxiety and activation were able to be differentiated in the investigated range of mean attentiveness. Anxious expectancy is perceived in particular as subjective anxiety. Fatigue and sedation, on the other hand, demonstrate subjective and autonomic desactivation. Corresponding differences can be demonstrated for the anxiolytic and sedative effects of tranquilizers. The time course of habituation is a more exact indicator than the amplitude of the orienting response. Cognitively provoked apprehensiveness, thus, appears to be qualitatively different as compared to psychoautonomically caused anxieties of psychiatric disorders.     

A few thoughts on brain ROIs

Quantitative mapping of structural and functional connectivities in the human brain via non-invasive neuroimaging offers an exciting and unique opportunity to understand brain architecture. Because connectivity alterations are widely reported in a variety of brain diseases, assessment of structural and functional connectivities has emerged as a fundamental research area in clinical neuroscience. A fundamental question arises when attempting to map structural and functional connectivities: how to define and localize the best possible Regions of Interests (ROIs) for brain connectivity mapping? Essentially, when mapping brain connectivities, ROIs provide the structural substrates for measuring connectivities within individual brains and for pooling data across populations. Thus, identification of reliable, reproducible and accurate ROIs is critically important for the success of brain connectivity mapping. This paper discusses several major challenges in defining optimal brain ROIs from our perspective and presents a few thoughts on how to deal with those challenges based on recent research work done in our group.