We have studied the shape of rabbit ciliary ganglion cells in relation to the number of axons that innervate each neuron. Adult ganglion cells receive synapses from one to seven different pregan- glionic axons. Some neurons lack dendrites...
moreWe have studied the shape of rabbit ciliary ganglion cells in relation to the number of axons that innervate each neuron. Adult ganglion cells receive synapses from one to seven different pregan- glionic axons. Some neurons lack dendrites altogether, whereas others have complex arborizations of up to eight primary dendrites. The neurons that receive all of their synaptic contacts from
We have undertaken a quantitative analysis of the mouse olfactory bulb to address several major questions concerning the development of neural circuitry in the postnatal mammalian brain. These are: (1) To what degree are new elements and...
moreWe have undertaken a quantitative analysis of the mouse olfactory bulb to address several major questions concerning the development of neural circuitry in the postnatal mammalian brain. These are: (1) To what degree are new elements and circuits added during maturation? (2) How long do such processes go on? and (3) Does postnatal development involve a net addition of circuits and their constituent elements, or is there elimination of some portion of an initial surfeit? Using male mice of known age, weight, and length, we measured the overall size of the bulb, the numbers of processing units (glomeruli) within the bulb, the extent and complexity of postsynaptic dendrites within the glomeruli, and the number of synapses in different regions of the bulb. Between birth and the time mice reach sexual maturity at 6-7 weeks of age, the bulb increases in size by a factor of 8, the number of glomeruli by a factor of 4-5, the length of mitral cell dendritic branches by a factor of 11, and the number of glomerular and extraglomerular synapses by factors of 90 and 170, respectively. Each of these parameters increases steadily from birth, in concert with the enlargement of the olfactory mucosa, the overall growth of the brain, and indeed, of the entire animal. We found no evidence of an initial surfeit of processing units, dendritic branches, or synapses. Further elaboration of neural circuitry by each of these measures is also apparent from the time of sexual maturity until the animals reach their full adult size at about 10-12 weeks of age. The developmental strategy in this part of the mouse brain evidently involves prolonged construction that persists until the growth of the body is complete. This ongoing elaboration of neural circuitry in the postnatal mammalian brain may be relevant to understanding a number of unexplained developmental phenomena, including critical periods, the ability of the juvenile brain to recover from injuries that would cause severe and permanent deficits in older animals, and the special ability of the maturing brain to encode large amounts of new information.
We have compared the size and arrangement of the primary somatic sensory cortex (SI) and its constituent parts in juvenile (1 week old) and mature (10-12 weeks old) rats using succinic dehydrogenase histochemistry and digital image...
moreWe have compared the size and arrangement of the primary somatic sensory cortex (SI) and its constituent parts in juvenile (1 week old) and mature (10-12 weeks old) rats using succinic dehydrogenase histochemistry and digital image analysis. Our goal was to determine whether some regions of the maturing cortex grow more than others. To this end, we examined (1) the growth of barrels and the surrounding (interbarrel) cortex, (2) the growth of the major somatic representations within SI, and (3) the overall growth of SI compared to the neocortex as a whole. With respect to the first of these issues, SI barrels and barrel-like structures grow more than the intervening cortex. The growth of these elements varies according to region: barrels in the head representation more than double in size, whereas the barrel-like structures in the paw representations increase by only about half this amount. The growth of the major somatic representations within SI is also heterogeneous, the represent...
The colors perceived by humans in response to light stimuli are generally described in terms of four color categories (reds, greens, blues and yellows), the members of which are systematically arrayed around gray. This broadly accepted...
moreThe colors perceived by humans in response to light stimuli are generally described in terms of four color categories (reds, greens, blues and yellows), the members of which are systematically arrayed around gray. This broadly accepted description of color sensation differs fundamentally from the light that induces it, which is neither 'circular' nor categorical. What, then, accounts for these discrepancies between the structure of color experience and the physical reality that underlies it? We suggest that these differences are based on two related requirements for successful color vision: (1) that spectra be ordered according to their physical similarities and differences; and (2) that this ordering be constrained by the four-color map problem.
Observation of human subjects shows that the spectral returns of equiluminant colored surrounds govern the apparent brightness of achromatic test targets. The influence of color on brightness provides further evidence that perceptions of...
moreObservation of human subjects shows that the spectral returns of equiluminant colored surrounds govern the apparent brightness of achromatic test targets. The influence of color on brightness provides further evidence that perceptions of luminance are generated according to the empirical frequency of the possible sources of visual stimuli, and suggests a novel way of understanding color contrast and constancy.
We have evaluated the efficacy of 18 cationic mitochondrial dyes that, as a class, show some ability to stain living nerve terminals. Several of these agents provide excellent stain- ing of neuromuscular junctions in a wide range of...
moreWe have evaluated the efficacy of 18 cationic mitochondrial dyes that, as a class, show some ability to stain living nerve terminals. Several of these agents provide excellent stain- ing of neuromuscular junctions in a wide range of species. More detailed studies of the most effective of these dyes- 4-(4-diethylaminostyryl)~Kmethylpyridinium iodide (4-Di-2-
The enormous range of animal size raises a fundamental problem: How do larger animals maintain adequate control of peripheral structures that are many times more massive and extensive than the homologous structures in smaller animals? To...
moreThe enormous range of animal size raises a fundamental problem: How do larger animals maintain adequate control of peripheral structures that are many times more massive and extensive than the homologous structures in smaller animals? To explore this question, we have determined neuronal number, the number of axons that innervate each neuron (convergence) and the number of neurons innervated by each axon (divergence), in a peripheral sympathetic pathway of several mammals (mouse, hamster, rat, guinea pig, and rabbit). The average adult weights of these species vary over approximately a 65-fold range. However, the number of superior cervical ganglion cells increases by only a factor of 4 between the smallest of these animals (mice; about 25 gm) and the largest (rabbits; about 1700 gm); the number of spinal preganglionic neurons that innervate the ganglion increases by only a factor of 2. Thus, the number of nerve cells in the sympathetic system does not increase in proportion to anim...
A remarkable feature of nerve cells is the complex and variable pattern of their axonal and dendritic branches. Quantitative studies of a simple part of the nervous system in mammals provide evidence that neuronal geometry and innervation...
moreA remarkable feature of nerve cells is the complex and variable pattern of their axonal and dendritic branches. Quantitative studies of a simple part of the nervous system in mammals provide evidence that neuronal geometry and innervation are regulated by long-term trophic interactions between neurons and their targets. This trophic linkage may explain how nerve cells adjust their function to the needs of bodies that vary markedly in size and form.
The phenomenology of pitch has been difficult to rationalize and remains the subject of much debate. Here we test the hypothesis that audition generates pitch percepts by relating inherently ambiguous sound stimuli to their probable...
moreThe phenomenology of pitch has been difficult to rationalize and remains the subject of much debate. Here we test the hypothesis that audition generates pitch percepts by relating inherently ambiguous sound stimuli to their probable sources in the human auditory environment. A database of speech sounds, the principal source of periodic sound energy for human listeners, was compiled and the dominant periodicity of each speech sound determined. A set of synthetic test stimuli were used to assess whether the major pitch phenomena described in the literature could be explained by the probabilistic relationship between the stimuli and their probable sources (i.e., speech sounds). The phenomena tested included the perception of the missing fundamental, the pitch-shift of the residue, spectral dominance and the perception of pitch strength. In each case, the conditional probability distribution of speech sound periodicities accurately predicted the pitches normally heard in response to the test stimuli. We conclude from these findings that pitch entails an auditory process that relates inevitably ambiguous sound stimuli to their probable natural sources.
The similarity of musical scales and consonance judgments across human populations has no generally accepted explanation. Here we present evidence that these aspects of auditory perception arise from the statistical structure of naturally...
moreThe similarity of musical scales and consonance judgments across human populations has no generally accepted explanation. Here we present evidence that these aspects of auditory perception arise from the statistical structure of naturally occurring periodic sound stimuli. An analysis of speech sounds, the principal source of periodic sound stimuli in the human acoustical environment, shows that the probability distribution of amplitude-frequency combinations in human utterances predicts both the structure of the chromatic scale and consonance ordering. These observations suggest that what we hear is determined by the statistical relationship between acoustical stimuli and their naturally occurring sources, rather than by the physical parameters of the stimulus per se.
Much current vision research is predicated on the idea—and a rapidly growing body of evidence—that visual percepts are generated according to the empirical significance of light stimuli rather than their physical characteristics. As a...
moreMuch current vision research is predicated on the idea—and a rapidly growing body of evidence—that visual percepts are generated according to the empirical significance of light stimuli rather than their physical characteristics. As a result, an increasing number of investigators have asked how visual perception can be rationalized in these terms. Here, we compare two different theoretical frameworks for predicting
We have analyzed blood vessel distribution in the primary and secondary visual cortices of the squirrel monkey in re- lation to cortical modules, laminae, and cytoarchitectonic areas. Measurements of microvessel length in tangential...
moreWe have analyzed blood vessel distribution in the primary and secondary visual cortices of the squirrel monkey in re- lation to cortical modules, laminae, and cytoarchitectonic areas. Measurements of microvessel length in tangential sections through the primary visual cortex showed that blobs are more richly vascularized than intervening cortical regions. Thus, the mean total length of microvessel profiles per unit was 42% greater within these cortical modules than within adjacent (interblob) areas. Total microvessel length per unit area in another class of module, the stripes in the sec- ondary visual cortex, was 27% greater than in interstripe regions. Microvessel distribution also varied systematically from layer to layer in the primary visual cortex, being greatest in lamina IVc. Finally, the overall microvessel length per unit area in sections of the primary visual cortex was 26% greater than that in the secondary visual cortex. These observations indicate that the modular, lam...
We describe a means of visualizing the same neuron in the superior cervical ganglion of young adult mice over intervals of up to 3 months. The dendrites of these neurons change during this interval; some branches retract, others elongate,...
moreWe describe a means of visualizing the same neuron in the superior cervical ganglion of young adult mice over intervals of up to 3 months. The dendrites of these neurons change during this interval; some branches retract, others elongate, and still others appear to form de novo. Thus, neuronal dendrites in this part of the nervous system are subject to continual change beyond what is usually considered the developmental period. The remodeling of postsynaptic processes further implies that the synaptic connections made onto these cells undergo substantial rearrangement well into adulthood.
We have examined several components of the human visual system to determine how the dimensions of the optic tract, lateral geniculate nucleus (LGN), and primary visual cortex (V1) vary within the same brain. Measurements were made of the...
moreWe have examined several components of the human visual system to determine how the dimensions of the optic tract, lateral geniculate nucleus (LGN), and primary visual cortex (V1) vary within the same brain. Measurements were made of the cross-sectional area of the optic tract, the volumes of the magnocellular and parvocellular layers of the LGN, and the surface area and
whether regenerating axon terminals reoccupy original syn- aptic sites. The distribution of synapses observed on the same neuronal cell bodies was almost always different in appearance after reinnervation. These results are at odds with...
morewhether regenerating axon terminals reoccupy original syn- aptic sites. The distribution of synapses observed on the same neuronal cell bodies was almost always different in appearance after reinnervation. These results are at odds with the conclusions of earlier workers, who have argued that mammalian neurons bear a fixed number of synaptic sites, which are reoccupied during reinnervation.
... 6, 16-20 81 Parnes, S., Karpati, (3, Carpenter, S., Kim, NMKNY, Wolfe, LS and Suranyi, L. (1985)Arch. Neurol. ... An apparent striatal gliosis invari-ably occurs in HD, in the sense that the number of glia per micro-scope field...
more... 6, 16-20 81 Parnes, S., Karpati, (3, Carpenter, S., Kim, NMKNY, Wolfe, LS and Suranyi, L. (1985)Arch. Neurol. ... An apparent striatal gliosis invari-ably occurs in HD, in the sense that the number of glia per micro-scope field increases. ...
The distribution of presynaptic endings on the surfaces of autonomic ganglion cells was mapped in living mice after intravenous administration of a styryl pyridinium dye. The staining and imaging techniques did not appear to damage the...
moreThe distribution of presynaptic endings on the surfaces of autonomic ganglion cells was mapped in living mice after intravenous administration of a styryl pyridinium dye. The staining and imaging techniques did not appear to damage the ganglion cells, or the synapses on them; these procedures could therefore be repeated after an arbitrary period. Observations of the same neurons at intervals of up to 3 weeks indicate that the pattern of preganglionic terminals on many of these nerve cells gradually changes.
Reduction of the number of axons that contact target cells may be a general feature of neural development. This process may underlie the progressively restricted malleability of the maturing nervous system.
The dendritic arbors of sympathetic neurons in different species of mammals vary systematically: the superior cervical ganglion cells of smaller mammals have fewer and less extensive dendrites than the homologous neurons in larger...
moreThe dendritic arbors of sympathetic neurons in different species of mammals vary systematically: the superior cervical ganglion cells of smaller mammals have fewer and less extensive dendrites than the homologous neurons in larger animals. This difference in dendritic complexity according to body size is reflected in the convergence of ganglionic innervation; the ganglion cells of progressively larger mammals are innervated by progressively more axons. These relations have implications both for the function of homologous neural systems in animals of different sizes and for the regulation of neuronal geometry during development.
Volumetric measurements show that right-handed individuals have larger right hands than left hands. In contrast, the hands of left-handers are much more nearly symmetrical. Based on what is known about trophic interactions between neurons...
moreVolumetric measurements show that right-handed individuals have larger right hands than left hands. In contrast, the hands of left-handers are much more nearly symmetrical. Based on what is known about trophic interactions between neurons and targets, these findings predict a corresponding asymmetry of the relevant parts of the sensorimotor system in right-handers. The lack of an opposite-hand asymmetry among left-handers further implies that right- and left-handed phenotypes do not arise according to the same developmental rules.
The striking illusions produced by simultaneous brightness contrast generally are attributed to the center-surround receptive field organization of lower order neurons in the primary visual pathway. Here we show that the apparent...
moreThe striking illusions produced by simultaneous brightness contrast generally are attributed to the center-surround receptive field organization of lower order neurons in the primary visual pathway. Here we show that the apparent brightness of test objects can be either increased or decreased in a predictable manner depending on how light and shadow are portrayed in the scene. This evidence suggests that perceptions of brightness are generated empirically by experience with luminance relationships, an idea whose implications we pursue in the accompanying paper.
It has been known for more than 40 years that images fade from perception when they are kept at the same position on the retina by abrogating eye movements. Although aspects of this phenomenon were described earlier, the use of...
moreIt has been known for more than 40 years that images fade from perception when they are kept at the same position on the retina by abrogating eye movements. Although aspects of this phenomenon were described earlier, the use of close-fitting contact lenses in the 1950s made possible a series of detailed observations on eye movements and visual continuity. In the intervening decades, many investigators have studied the role of image motion on visual perception. Although several controversies remain, it is clear that images deteriorate and in some cases disappear following stabilization; eye movements are, therefore, essential to sustained exoptic vision. The time course of image degradation has generally been reported to be a few seconds to a minute or more, depending upon the conditions. Here we show that images of entoptic vascular shadows can disappear in less than 80 msec. The rapid vanishing of these images implies an active mechanism of image erasure and creation as the basis of normal visual processing.
In both humans and experimental animals, the ability to perceive contours that are vertically or horizontally oriented is superior to the perception of oblique angles. There is, however, no consensus about the developmental origins or...
moreIn both humans and experimental animals, the ability to perceive contours that are vertically or horizontally oriented is superior to the perception of oblique angles. There is, however, no consensus about the developmental origins or functional basis of this phenomenon. Here, we report the analysis of a large library of digitized scenes using image processing with orientation-sensitive filters. Our results
Many otherwise puzzling aspects of the way we see brightness, colour, orientation and motion can be understood in wholly empirical terms. The evidence reviewed here leads to the conclusion that visual percepts are based on patterns of...
moreMany otherwise puzzling aspects of the way we see brightness, colour, orientation and motion can be understood in wholly empirical terms. The evidence reviewed here leads to the conclusion that visual percepts are based on patterns of reflex neural activity shaped entirely by the past success (or failure) of visually guided behaviour in response to the same or a similar retinal stimulus. As a result, the images we see accord with what the sources of the stimuli have typically turned out to be, rather than with the physical properties of the relevant objects. If vision does indeed depend upon this operational strategy to generate optimally useful perceptions of inevitably ambiguous stimuli, then the underlying neurobiological processes will eventually need to be understood within this conceptual framework.
Abstract 1. Reports measurements of the human central sulcus suggesting that the region of the brain that governs the upper extremity does indeed differ in the 2 hemispheres. The cortical surface within the dorsolateral portion of the...
moreAbstract 1. Reports measurements of the human central sulcus suggesting that the region of the brain that governs the upper extremity does indeed differ in the 2 hemispheres. The cortical surface within the dorsolateral portion of the central sulcus of the brain was ...
The responses of 20 young adult emmetropes with normal color vision were measured on a battery of visual performance tasks. Using previously documented tests of known reliability, we evaluated orientation discrimination, contrast...
moreThe responses of 20 young adult emmetropes with normal color vision were measured on a battery of visual performance tasks. Using previously documented tests of known reliability, we evaluated orientation discrimination, contrast sensitivity, wavelength sensitivity, vernier acuity, direction-of-motion detection, velocity discrimination, and complex form identification. Performance varied markedly between individuals, both on a given test and when the scores from all tests were combined to give an overall indication of visual performance. Moreover, individual performances on tests of contrast sensitivity, orientation discrimination, wavelength discrimination, and vernier acuity covaried, such that proficiency on one test predicted proficiency on the others. These results indicate a wide range of visual abilities among normal subjects and provide the basis for an overall index of visual proficiency that can be used to determine whether the surprisingly large and coordinated size differences of the components of the human visual system (Andrews, Halpern, & Purves, 1997) are reflected in corresponding variations in visual performance.
he fact that the subtense of any acute angle is seen as being somewhat larger than the measured angle of the stimulus, whereas the subtense of any obtuse angle is seen as being somewhat smaller, was first reported by Wundt (1) and subse-...
morehe fact that the subtense of any acute angle is seen as being somewhat larger than the measured angle of the stimulus, whereas the subtense of any obtuse angle is seen as being somewhat smaller, was first reported by Wundt (1) and subse- quently by both Hering (2) and Helmholtz (3), all of whom surmised that these distortions might underlie
The visual information that reaches the eye cannot uniquely describe the physical world. Because light arising from different physical objects can stimulate the retina in the same way, the source of a light stimulus is inevitably...
moreThe visual information that reaches the eye cannot uniquely describe the physical world. Because light arising from different physical objects can stimulate the retina in the same way, the source of a light stimulus is inevitably ambiguous. For example, a large object far away and a small one closer by can generate exactly the same retinal image. The visual port of the brain resolves this ambiguity by assigning appropriate values of brightness, color and geometry to the things we see. Purves, Lotto and Nundy argue that this assignment is made on a wholly probabilistic basis: What observers see in any circumstance is simply what the stimulus has typically signified in the past, indicated by behavioral success or failure.