A multi-channel, implantable microdrive system for use with sharp, ultra-fine "Reitboeck" microelectrodes.
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Arrays of closely spaced quartz-insulated, platinum-tungsten microelectrodes are widely used to obtain acute recordings from chronically prepared subjects. These electrodes have excellent recording characteristics and can be fabricated to a wide variety of tip specifications. Typically, in such experiments, electrodes are introduced into, and removed from, the brain on a daily basis and, over many months of study, hundreds of penetrations may be made through an intact dura. This procedure has benefits as well as problems and risks. For some experimental aims, it might be desirable to leave the microelectrodes within the brain so that the penetrations could be continued on subsequent days. This would allow a more thorough and systematic exploration of the neurons that lie along the trajectory of each of the closely aligned electrodes and would minimize risks and preparation time associated with daily electrode insertions. Here we present a means for achieving this aim using arrays of sharp, flexible Reitboeck electrodes of extremely fine diameter (40-microm shaft diameter, pulled and ground to a fine tip). We show that these electrodes retain their excellent recording characteristics and can remain under microdrive control within the brain for periods of many months and, in one remarkable case, for >4 years. (+info)
Psychophysical measurements of illusion of the puffy circle.
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The strength of an illusion of curvature created by an equilateral triangle, square or pentagon inscribed in a circle has been measured in the psychophysical experiments. The arcs of the circle looked as if they were bowed outwards in the stimuli of various sizes, but, at a fixed diameter of the circumscribed circle, the triangles produced the strongest, and the pentagons, the weakest illusion. The strength of the illusion augmented with the stimulus diameter. Concave and convex sides of the inscribed figures caused less illusory effect than the straight ones. Similar distortions of the stimuli have been observed in the output of a neurophysiological model of spatial frequency filtering of images, and the computed curves resembled those of the experimental data, in respect to their shape and quantitative values. (+info)
In memorium: Herman p. Schwan [1915-2005].
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Herman P. Schwan [1915-2005] was a distinguished scientist and engineer, and a founding father of the field of biomedical engineering. A man of integrity, Schwan influenced the lives of many, including his wife and children, and his many students and colleagues. Active in science until nearly the end of his life, he will be very much missed by his family and many colleagues. (+info)
A neurologist looks at mind and brain: "the enchanted loom".
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For a long time, before we developed an appreciation of the neuroanatomy and neurophysiology of the brain, there was uncertainty as to the nature and source of the human mind. Philosophers linked the mind to mythical "humors" that controlled the human body, and others speculated that the mind was associated with "life-force" or soul. Few felt that there was a relation between the human mind and brain, but they had to wait for the Age of Enlightenment and scientific discovery in the 18th and 19th centuries to establish a clear association between the two. Three centuries ago Rene Descartes described the mind as an extracorporeal entity that was expressed through the pineal gland. Descartes was wrong about the pineal, but the debate he set off regarding the relationship between mind and brain rages on. This review looks at the history of speculation on the mind and the development of ideas that have led to our present understanding of this phenomenon. The basic anatomy and physiology of the brain is reviewed to help us understand the brain's association with the complex function we call mind. This is followed by a look at some syndromes that may result when part of the brain is damaged-the parietal lobe is arbitrarily selected as an example-and the resulting effect on the subject's mind. This assists us in understanding the association of mind and brain, and also to better understanding its components, behavior, function and dysfunction. (+info)
Transcranial magnetic stimulation in clinical practice.
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Transcranial magnetic stimulation allows a non-invasive and painless stimulation of the human brain and cranial nerves. The method is in use since 1985. Transcranial magnetic stimulation can use single stimuli, pairs of stimuli separated by different intervals (to the same or to several brain areas), or trains of repetitive stimuli at various frequencies. Single stimuli give rise to motor evoked potentials that have clinical use and serve diagnostic and prognostic purposes. Repetitive transcranial magnetic stimulation can modify excitability of cerebral cortex. Repetitive transcranial magnetic stimulation has opened a new field of investigation of the neural circuitry, and is developing into a therapeutic tool. This general review considers basic principles of transcranial magnetic stimulation, discusses methodological aspects and techniques, and analyses their utility in clinical practice. (+info)
From heart to mind. The urotensin II system and its evolving neurophysiological role.
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The discovery of novel biologically active peptides has led to an explosion in our understanding of the molecular mechanisms that underlie the regulation of sleep and wakefulness. Urotensin II (UII), a peptide originally isolated from fish and known for its strong cardiovascular effects in mammals, is another surprising candidate in the regulatory network of sleep. The UII receptor was found to be expressed by cholinergic neurons of laterodorsal and pedunculopontine tegmental nuclei, an area known to be of utmost importance for the on- and offset of rapid eye movement (REM) sleep. Recently, physiological data have provided further evidence that UII is indeed a modulator of REM sleep. The peptide directly excites cholinergic mesopontine neurons and increases the rate of REM sleep episodes. These new results and its emerging behavioral effects establish UII as a neurotransmitter/neuromodulator in mammals and should spark further interest into the neurobiological role of the peptide. (+info)
Single synaptic vesicle tracking in individual hippocampal boutons at rest and during synaptic activity.
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How synaptic vesicles move within central nervous synapses to their docking sites at the plasma membrane is widely discussed in synaptic physiology. This question is especially difficult to investigate in the small hippocampal boutons, which themselves can slowly move during observation in primary cell culture. Here, we describe a single particle tracking method using dual fluorescent dye labels that enabled us to visualize the movements of a single vesicle and the respective synaptic bouton simultaneously during resting conditions and stimulation. We found vesicle mobility to be very low in the absence of stimulation, in line with previous studies. Interestingly, mobility was also found to be low during synaptic activity. We found that vesicles labeled preferentially via early, late, and spontaneous endocytotic mechanisms behaved similarly at rest and during stimulation. (+info)
Neurophysiology of perceptual and motor aspects of interception.
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The interception of moving targets is a complex activity that involves a dynamic interplay of several perceptual and motor processes and therefore involves a rich interaction among several brain areas. Although the behavioral aspects of interception have been studied for the past three decades, it is only during the past decade that neural studies have been focused on this problem. In addition to the interception itself, several neural studies have explored, within that context, the underlying mechanisms concerning perceptual aspects of moving stimuli, such as optic flow and apparent motion. In this review, we discuss the wealth of knowledge that has accumulated on this topic with an emphasis on the results of neural studies in behaving monkeys. (+info)