Human cortical areas underlying the perception of optic flow: brain imaging studies

In summary, we have reviewed electrophysiological and brain imaging studies of motion and optic-flow processing. Single-unit studies indicate that MST (V5a) is a site of optic-flow extraction and that this information can be used to guide pursuit eye movements and to estimate heading. The EEG and MEG studies point to a localized electrical dipole in occipitotemporal cortex evoked by visual motion. We have also discussed the evidence from functional imaging studies for response specificity of the rCBF and BOLD effects in posterior cortex to visual motion and optic flow. Focal attention modulates the amplitude of the BOLD signal evoked by visual motion stimulation. Retinotopic mapping techniques have been used to locate region borders within the visual cortex. Our results indicate that striate (V1) and extrastriate areas (V2, V3/V3a) respond robustly to optic flow. However, with exception of a more pronounced response in V3/V3a to random walk, we found little evidence for response selectivity with respect to flow type and disparity in these early visual areas. In a similar fashion, the human V5/V5a complex responds well to optic flow, but these responses do not vary significantly with the type of flow field and do not seem to depend on disparity. In contrast, the kinetic occipital area (KO/V3b) responds well to optic-flow information, and it is the only area that produces more pronounced activation to the disparity in the flow fields. These initial results are promising because they suggest that the fMRI method can be sensitive to changes in stimulus parameters that define flow fields. More work will be required to explore the extent to which these responses reflect the neuronal processing of optic flow. Eye position tracking is now possible during fMRI experiments. We have demonstrated that the eye movements affect the BOLD responses in motion-sensitive areas (Kimming et al., 1999). Further experiments in our laboratory are aimed at understanding the effects of eye movements on the neuronal coding of complex optic-flow fields (Schira et al., 1999).

Sex differences in energy expenditure in non-human primates

Female mammals bear the energetic costs of gestation and lactation. Therefore, it is often assumed that the overall energetic costs are greater for females than they are for males. However, the energetic costs to males of intrasex competition may also be considerable, particularly if males maintain a much larger body size than females. Using data from 19 non-human primates, this paper examines the relationship between male and female energetic costs both in the short term (daily energy expenditure) and the long term (the energetic cost of producing a single offspring). It is shown that the major determinant of sex differences in energetic costs is body size dimorphism. In the long term, the energetic costs are often greater for females, but, when male body size exceeds female body size by 60% or more, male energetic costs are greater than those for females. That is, in highly sexually dimorphic species the energetic costs of gestation and lactation for the females are matched by the energetic costs to the males of maintaining a large body size.

Multiple single unit recording in the cortex of monkeys using independently moveable microelectrodes

Simultaneous recording from multiple single neurones presents many technical difficulties. However, obtaining such data has many advantages, which make it highly worthwhile to overcome the technical problems. This report describes methods which we have developed to permit recordings in awake behaving monkeys using the 'Eckhorn' 16 electrode microdrive. Structural magnetic resonance images are collected to guide electrode placement. Head fixation is achieved using a specially designed headpiece, modified for the multiple electrode approach, and access to the cortex is provided via a novel recording chamber. Growth of scar tissue over the exposed dura mater is reduced using an anti-mitotic compound. Control of the microdrive is achieved by a computerised system which permits several experimenters to move different electrodes simultaneously, considerably reducing the load on an individual operator. Neurones are identified as pyramidal tract neurones by antidromic stimulation through chronically implanted electrodes; stimulus control is integrated into the computerised system. Finally, analysis of multiple single unit recordings requires accurate methods to correct for non-stationarity in unit firing. A novel technique for such correction is discussed.

Taste in the monkey cortex

The sense of taste in humans differs substantially from that of rodents, from which a preponderance of gustatory electrophysiology derives. To establish a more appropriate neural model for human gustation, we recorded the activity of single neurons in the primary taste cortex in 11 alert cynomolgus macaques. Taste cells composed 6% of all neurons encountered. Another 24% responded during mouth and jaw movements, and 4% were sensitive to tactile stimulation of the mouth. Smaller numbers responded during olfactory or visual stimulation, or when the monkey extended his tongue. Taste cells could be divided into four statistically independent groups, corresponding to those most responsive to glucose (38%), NaCl (34%), quinine (22%), or HCI (5%). The location of a taste cell did not predict its response profile, i.e., there was no clear topographic organization of taste sensitivity. We established neural thresholds and intensity-response functions to the basic stimuli and determined that-with the exception of HCl, to which the macaque is relatively insensitive-they were similar to those reported by human subjects. We then turned to the coding of taste quality, as inferred in macaques from the patterns of neural activity elicited by each of greater than 100 stimuli. The results proved generally faithful to human reports of the perceived qualities of these same tastants. Finally, an investigation of taste mixtures revealed a degree of mixture suppression and interaction among basic qualities similar to those reported by humans. We conclude that the alert macaque offers a reliable neural model for human gustation.

Reflex pathways from large muscle spindle afferents and recurrent axon collaterals to motoneurones of wrist and digit muscles: a comparison in cats, monkeys and humans

Whereas a large body of data is available on the control of hand motoneurones from the brain, not much is known about the contribution of the spinal interneuronal apparatus to the differentiated movement repertoire of the hand. This review summarises recent data on the excitatory Ia pathways and on recurrent inhibition for cats, monkeys and humans. The basic principles of organisation have, in general, been preserved in the different species. Thus the motoneurones to cat and human long and short digit muscles seem not to possess a recurrent axon collateral system. With regard to the Ia pathways, specialised connectivity patterns have developed in the long digit extensor and wrist extensor muscles. They allow the former group to support the differentiated movement repertoire of the digits, and the latter group to be part of a general extensor or flexor synergism. Modifications between the species are present, however, with regard to the proximodistal connectivity across the elbow. Whereas they are regularly present in the cat, they are less developed in the monkey and absent in man, which frees the human hand from the elbow position.

Neuronal responses to orientation and motion contrast in cat striate cortex

Responses of striate neurons to line textures were investigated in anesthetized and paralyzed adult cats. Light bars centered over the excitatory receptive field (RF) were presented with different texture surrounds composed of many similar bars. In two test series, responses of 169 neurons to textures with orientation contrast (surrounding bars orthogonal to the center bar) or motion contrast (surrounding bars moving opposite to the center bar) were compared to the responses to the corresponding uniform texture conditions (all lines parallel, coherent motion) and to the center bar alone. In the majority of neurons center bar responses were suppressed by the texture surrounds. Two main effects were found. Some neurons were generally suppressed by either texture surround. Other neurons were less suppressed by texture displaying orientation or motion (i.e. feature) contrast than by the respective uniform texture, so that their responses to orientation or motion contrast appeared to be relatively enhanced (preference for feature contrast). General suppression was obtained in 33% of neurons tested for orientation and in 19% of neurons tested for motion. Preference for orientation or motion contrast was obtained in 22% and 34% of the neurons, respectively, and was also seen in the mean response of the population. One hundred nineteen neurons were studied in both orientation and motion tests. General suppression was correlated across the orientation and motion dimension, but not preference for feature contrast. We also distinguished modulatory effects from end-zones and flanks using butterfly-configured texture patterns. Both regions contributed to the generally suppressive effects. Preference for orientation or motion contrast was not generated from either end-zones or flanks exclusively. Neurons with preference for feature contrast may form the physiological basis of the perceptual saliency of pop-out elements in line textures. If so, pop-out of motion and pop-out of orientation would be encoded in different pools of neurons at the level of striate cortex.

Interview with John Kaas

Jon Kaas received a Ph.D. in Psychology with Irving Diamond at Duke University and completed a postdoctoral fellowship with Clinton Woolsey in neurophysiology at the University of Wisconsin, where he also collaborated with Ray Guillery. After 4 years as an Assistant Professor in Neurophysiology at Wisconsin, he moved to the Department of Psychology at Vanderbilt University where he is currently Centennial Professor. Awards include the Earl Sutherland Prize, Javits Neuroscience Investigator Award, Krieg Cortical Discoverer Award, and American Psychological Association Distinguished Scientific Contribution Award.

Grasping objects and grasping action meanings: the dual role of monkey rostroventral premotor cortex (area F5)

Monkey area F5 consists of two main histochemical sectors, one buried inside the arcuate sulcus, the other located on the cortical convexity. Neurons of both sectors discharge during hand movements. Many of them also fire in response to the presentation of visual stimuli. However, the visual stimuli effective for triggering the neurons in each sector are markedly different. Neurons located in the bank of the arcuate sulcus respond to the observation of 3D objects, provided that object size and shape is congruent with the prehension type coded by the neuron ('canonical' F5 neurons). Neurons of the convexity discharge when the monkey observes hand actions performed by another individual, provided that they are similar to the motor action coded by the neuron ('mirror' neurons). What do the canonical F5 neurons and the surprising mirror neurons have in common? The interpretation we propose is that these two categories of F5 neurons both generate an internal copy of a potential hand action. In the case of 'canonical' neurons, this copy gives a description of how to grasp an object; in the case of mirror neurons it gives a description of an action made by another person. Because the individuals know the consequences of their actions, we propose that the internal motor copies of the observed actions represent the neural basis for understanding the meaning of actions made by others.

Neurology of saccades and smooth pursuit

During the period covered by this review a number of papers have been published on saccade and smooth pursuit research, conducted experimentally in monkeys and clinically in humans. In monkeys, using mainly electrophysiological methods, the roles of the frontal eye field, parietal eye field and supplementary eye field at the cortical level, and those of the paramedian pontine reticular formation, nucleus prepositus hypoglossi, interstitial nucleus of Cajal and superior colliculus at the brainstem level have been studied in great detail. In humans the same cortical areas have also been examined, mainly using functional imaging resulting in new information on the location of these areas and new hypotheses on the role of the superior parietal lobule in visual attention and that of the posterior part of the anterior cingulate cortex in motivation. Saccades, smooth pursuit and clinical applications of eye movement research are dealt with separately.

Recent advances in noninvasive techniques to monitor hormone-behavior interactions

This paper reviews recent advances in field endocrinology, a focus as well as a method in primatology and behavioral ecology that permits the examination of social behavior and life history through hormonal investigations in natural settings. Endocrine data complements the traditional behavioral data collected by field scientists by providing quantitative measures for the examination of adaptive tradeoffs, costs of social strategies, and reproductive and social significance of mating events. Further, investigations of the physiological mechanisms of reproductive constraint provide tests of the adaptive significance of reproductive skew in cooperative and competitive breeders. Hormone data also can provide insights into the costs of competition and aggression and the role of temperament in individual reproductive success and the evolution of social systems. New, noninvasive methods for the collection of this information have augmented and expanded field endocrinology through the use of techniques that do not require potentially confounding physical or physiological manipulations. Specifically, urine and fecal samples can be collected from free-ranging animals and contain gonadal and adrenal hormones that parallel profiles of serum hormones. Sampling, preservation, extraction, and assay methods for the analysis of excreted steroids are reviewed along with the species and questions to which these methods have been applied.

Single units and conscious vision

Figures that can be seen in more than one way are invaluable tools for the study of the neural basis of visual awareness, because such stimuli permit the dissociation of the neural responses that underlie what we perceive at any given time from those forming the sensory representation of a visual pattern. To study the former type of responses, monkeys were subjected to binocular rivalry, and the response of neurons in a number of different visual areas was studied while the animals reported their alternating percepts by pulling levers. Perception-related modulations of neural activity were found to occur to different extents in different cortical visual areas. The cells that were affected by suppression were almost exclusively binocular, and their proportion was found to increase in the higher processing stages of the visual system. The strongest correlations between neural activity and perception were observed in the visual areas of the temporal lobe. A strikingly large number of neurons in the early visual areas remained active during the perceptual suppression of the stimulus, a finding suggesting that conscious visual perception might be mediated by only a subset of the cells exhibiting stimulus selective responses. These physiological findings, together with a number of recent psychophysical studies, offer a new explanation of the phenomenon of binocular rivalry. Indeed, rivalry has long been considered to be closely linked with binocular fusion and stereopsis, and the sequences of dominance and suppression have been viewed as the result of competition between the two monocular channels. The physiological data presented here are incompatible with this interpretation. Rather than reflecting interocular competition, the rivalry is most probably between the two different central neural representations generated by the dichoptically presented stimuli. The mechanisms of rivalry are probably the same as, or very similar to, those underlying multistable perception in general, and further physiological studies might reveal much about the neural mechanisms of our perceptual organization.

The role of prefrontal cortex in working memory: examining the contents of consciousness

Working memory enables us to hold in our 'mind's eye' the contents of our conscious awareness, even in the absence of sensory input, by maintaining an active representation of information for a brief period of time. In this review we consider the functional organization of the prefrontal cortex and its role in this cognitive process. First, we present evidence from brain-imaging studies that prefrontal cortex shows sustained activity during the delay period of visual working memory tasks, indicating that this cortex maintains on-line representations of stimuli after they are removed from view. We then present evidence for domain specificity within frontal cortex based on the type of information, with object working memory mediated by more ventral frontal regions and spatial working memory mediated by more dorsal frontal regions. We also propose that a second dimension for domain specificity within prefrontal cortex might exist for object working memory on the basis of the type of representation, with analytic representations maintained preferentially in the left hemisphere and image-based representations maintained preferentially in the right hemisphere. Furthermore, we discuss the possibility that there are prefrontal areas brought into play during the monitoring and manipulation of information in working memory in addition to those engaged during the maintenance of this information. Finally, we consider the relationship of prefrontal areas important for working memory, both to posterior visual processing areas and to prefrontal areas associated with long-term memory.

Origins and antiquity of X-linked triallelic color vision systems in New World monkeys

It is known that the squirrel monkey, marmoset, and other related New World (NW) monkeys possess three high-frequency alleles at the single X-linked photopigment locus, and that the spectral sensitivity peaks of these alleles are within those delimited by the human red and green pigment genes. The three alleles in the squirrel monkey and marmoset have been sequenced previously. In this study, the three alleles were found and sequenced in the saki monkey, capuchin, and tamarin. Although the capuchin and tamarin belong to the same family as the squirrel monkey and marmoset, the saki monkey belongs to a different family and is one of the species that is most divergent from the squirrel monkey and marmoset, suggesting the presence of the triallelic system in many NW monkeys. The nucleotide sequences of these alleles from the five species studied indicate that gene conversion occurs frequently and has partially or completely homogenized intronic and exonic regions of the alleles in each species, making it appear that a triallelic system arose independently in each of the five species studied. Nevertheless, a detailed analysis suggests that the triallelic system arose only once in the NW monkey lineage, from a middle wavelength (green) opsin gene, and that the amino acid differences at functionally critical sites among alleles have been maintained by natural selection in NW monkeys for >20 million years. Moreover, the two X-linked opsin genes of howler monkeys (a NW monkey genus) were evidently derived from the incorporation of a middle (green) and a long wavelength (red) allele into one chromosome; these two genes together with the (autosomal) blue opsin gene would immediately enable even a male monkey to have trichromatic vision.

Computational modelling of optic flow selectivity in MSTd neurons

In neurophysiological experiments examining the selectivity of MSTd neurons to visual motion components of optic flow stimuli in monkeys, Duffy and Wurtz (1991) reported cells with double-component (plano-radial and plano-circular) and triple-component (plano-radial-circular) selectivities, while Graziano et al (1994) reported neurons selective to a continuum of optic flow stimuli including spiral motion. Here, we address these reported findings under simulated experimental conditions by examining the development of optic flow selectivity in the hidden units of a two-layer back-propagation network. We also examine network motion sensitivity during simulated psychophysical tests via the addition of a competitive decision layer. Network analysis with neurophysiological stimuli identified a majority of hidden units whose position invariance and motion selectivity were consistent with MSTd responses to the visual motion components of optic flow stimuli reported by Duffy and Wurtz and Graziano et al. Furthermore, the hidden units developed a continuum of optic flow selectivities independent of the biases associated with the specification of the motion selectivity in the output layer. During psychophysical testing, network responses showed motion sensitivities which met or exceeded human performance. Within the limitations imposed by the learning algorithm, the psychophysical results were consistent with a model of global motion perception via local integration along complex motion trajectories.

Idiothetic input into object-place configuration as the contribution to memory of the monkey and human hippocampus: a review

Memory for object-place configurations appears to be a common function of the hippocampus in the human and monkey brain. The nature of the spatial information which enters into these object-configural memories in the primate, and the location of the memories themselves, have remained obscure, however. In the rat, much evidence indicates that the hippocampus processes idiothetic spatial information, an estimate of the animal's current environmental location derived from path integration. I propose that in primates the hippocampus provides idiothetic information about the environmental location of body parts, and that the main function of this information in the primate brain is to become configured with object-identity information provided by temporal lobe cortex outside the hippocampus.

Is there a geniculohypothalamic tract in primates? A comparative immunohistochemical study in the circadian system of strepsirhine and haplorhine species

In rodents, the circadian rhythm generated by the hypothalamic suprachiasmatic nucleus (SCN) is modulated by two types of phenomena: photic phase-shifts, mediated by the retinohypothalamic pathway and non-photic phase-shifts mediated by the projection of the intergeniculate leaflet (IGL) to the SCN which contains the neuropeptide Y (NPY). In primates, the retinohypothalamic pathway has been well-demonstrated but very little is known about the geniculohypothalamic tract. This prompted us to study NPY immunoreactivity in both the SCN and the IGL in species representative of the three main primate lineages: prosimians (Microcebus), New World monkeys (Callithrix) and Old World monkeys (Macacca). In species studied, we found a region in the pregeniculate nucleus containing both NPY immunopositive cells and substance P immunopositive fibres that we identified as the IGL. During evolution, this structure has moved from a ventral to a dorsomedial position relative to the adjacent dorsal lateral geniculate nucleus. By contrast, NPY-IP fibres in the SCN are dense in prosimians, but are sparse or absent in other primate species. We suggest that either the geniculohypothalamic projection is absent in higher primates as is the case in humans, or is absent in diurnal mammals, or contains a different peptide, or that NPY immunoreactivity varies according to other parameters.

Neural coding of 3D features of objects for hand action in the parietal cortex of the monkey

In our previous studies of hand manipulation task-related neurons, we found many neurons of the parietal association cortex which responded to the sight of three-dimensional (3D) objects. Most of the task-related neurons in the AIP area (the lateral bank of the anterior intraparietal sulcus) were visually responsive and half of them responded to objects for manipulation. Most of these neurons were selective for the 3D features of the objects. More recently, we have found binocular visual neurons in the lateral bank of the caudal intraparietal sulcus (c-IPS area) that preferentially respond to a luminous bar or place at a particular orientation in space. We studied the responses of axis-orientation selective (AOS) neurons and surface-orientation selective (SOS) neurons in this area with stimuli presented on a 3D computer graphics display. The AOS neurons showed a stronger response to elongated stimuli and showed tuning to the orientation of the longitudinal axis. Many of them preferred a tilted stimulus in depth and appeared to be sensitive to orientation disparity and/or width disparity. The SOS neurons showed a stronger response to a flat than to an elongated stimulus and showed tuning to the 3D orientation of the surface. Their responses increased with the width or length of the stimulus. A considerable number of SOS neurons responded to a square in a random dot stereogram and were tuned to orientation in depth, suggesting their sensitivity to the gradient of disparity. We also found several SOS neurons that responded to a square with tilted or slanted contours, suggesting their sensitivity to orientation disparity and/or width disparity. Area c-IPS is likely to send visual signals of the 3D features of an object to area AIP for the visual guidance of hand actions.

Effects of syllable duration on stop-glide identification in syllable-initial and syllable-final position by humans and monkeys

Humans and monkeys were compared in their identification of phoneme boundaries along synthetic stop-glide continua in syllable-initial /bo/-/wa/ or syllable-final /bab/-/baw/ contrasts differing in overall syllable duration. For both contrasts, humans were first tested with a conventional written identification procedure. Here, similar phoneme boundaries emerged and shifted with increases in syllable duration toward longer transitions, as has previously been reported in the literature for syllable-initial data (Miller & Liberman, 1979). Humans and monkeys were then tested on these contrasts, using a go/no-go identification procedure specifically designed for monkeys. Here also, stop-glide boundaries emerged and shifted with increased syllable duration for both species, although monkey "boundaries" were at longer durations than humans' in syllable-final position. The results indicate that there are both gross similarities and subtle differences between humans and monkeys with regard to the stop-glide context effect. The results are discussed in relation to the hypothesis that general mammalian auditory mechanisms are responsible for this effect.

How it is to be the brain of a monkey

Hypotheses are presented on neural peculiarities of the monkey brain that distinguish monkeys from other mammals and man: The unique feature of cortical tissue is that it can be applied serially. It fulfils some requirements of a powerful visual system. The richness of visual as compared to other signals has yielded a basis for recognizing the bodily similarity of oneself to conspecifics. A visuo/motor coupling trained on oneself but applied to conspecifics ("aping") evolved. Long series of (generalized visuo/visual) computations feasible in a very large cortex would produce excessive delays that would not correspond to outer world delays. The new human solution to this is an "offline" system in which temporal relationships are described by excitation patterns. This gives rise to a rapid expansion of the cortex. In humans, a "meaning" has to be attributed to the mutual (computational) relationships of excitation patterns in the offline system, by a reference to the corresponding relationships that would be valid in the normal (online) system. "Perception" is a corollary of this. The offline treatment of time, together with "aping", leads to new types of helping and other social interactions. Monkeys may be compared to humans not using their offline system in the state of "absent-mindedness". Experimental approaches departing from excitation patterns are discussed.

The neuronal machinery involved in successive orientation discrimination

Following our strategy of using simple discrimination tasks to investigate the primate visual system, we trained both human and monkey subjects for two orientation discrimination tasks: an identification and a successive discrimination. Contrasting these two tasks allowed us to isolate the temporal comparison component and to relate this component to activity in right fusiform gyrus using Positron Emission Tomography (PET) and to infero-temporal cortex using a lesion approach in monkeys. Single-cell recordings in infero-temporal cortex demonstrated that neurons in this region can contribute to the three processes underlying temporal comparison: (1) sensorial representation of visual stimuli, (2) maintaining a trace of the preceding stimulus, and (3) comparison of the incoming stimulus with that trace. By the same token, a comparison of these two tasks, which use the same input and the same attribute, demonstrates the task dependency of processing in the human and non-human primate visual system.

A comparative immunohistochemical study of pancreatic islets in laboratory animals (rats, dogs, minipigs, nonhuman primates)

The aim of the present study was to distinguish and describe the patterns of distribution of pancreatic islets within the pancreas of four species of laboratory animals, including rats, dogs, minipigs and monkeys, and furthermore, to identify immunohistochemically various islet cell types and characterize their content. Histopathological examinations were performed on sections stained with hematoxylin and eosin (H&E) and immunostained using rabbit polyclonal antibodies (pAb) against insulin, glucagon, pancreatic polypeptide (PP), somatostatin, chromogranin A, keratin, bombesin and gastrin, or mouse monoclonal antibodies (mAb) against synaptophysin, Leu-7 and proliferating cell nuclear antigen (PCNA) in three-step rabbit immunoperoxidase (PAP) and streptavidin/peroxidase (StreptABC/HRP) reactions. Positive immunohistochemical reactions were observed in the pancreatic islets of all animal species with all antibodies, except with anti-bombesin and anti-gastrin antibodies. Our results revealed that: 1) there is species specific regional arrangement of islets in the pancreas, 2) each species presents a characteristic distribution of cells producing different hormones. 3) immunoreactivity with immunohistochemical markers varies between species and/or age. The present comparative immunohistochemical study could be helpful for answering questions which are important for understanding some of the intricate mechanisms that govern the integrated function of the endocrine pancreas.

Impact of temporal variation and the balance between excitation and inhibition on the output of the perfect integrate-and-fire model

We consider how the output of the perfect integrate-and-fire (I&F) model of a single neuron is affected by the properties of the input, first of all by the distribution of afferent excitatory and inhibitory postsynaptic potential (EPSP, IPSP) inter-arrival times, discriminating particularly between short- and long-tailed forms, and by the degree of balance between excitation and inhibition (as measured by the ratio, r, between the numbers of inhibitory and excitatory inputs). We find that the coefficient of variation (CV; standard deviation divided by mean) of efferent interspike interval (ISI) is an increasing function of the length of the tail of the distribution of EPSP inter-arrival times and the ratio r. There is a range of values of r in which the CV of output ISIs is between 0.5 and 1. Too tight a balance between EPSPs and IPSPs will cause the model to produce a CV outside the interval considered to correspond to the physiological range. Going to the extreme, an exact balance between EPSPs and IPSPs as considered in [24] ensures a long-tailed ISI output distribution for which the moments such as mean and variance cannot be defined. In this case it is meaningless to consider quantities like output jitter, CV, etc. of the efferent ISIs. The longer the tail of the input inter-arrival time distribution, the less is the requirement for balance between EPSPs and IPSPs in order to evoke output spike trains with a CV between 0.5 and 1. For a given short-tailed input distribution, the range of values of r in which the CV of efferent ISIs is between 0.5 and 1 is almost completely inside the range in which output jitter (standard deviation of efferent ISI) is greater than input jitter. Only when the CV is smaller than 0.5 or the input distribution is a long-tailed one is output less than input jitter [21]. The I&F model tends to enlarge low input jitter and reduce high input jitter. We also provide a novel theoretical framework, based upon extreme value theory in statistics, for estimating output jitter, CV and mean firing time.

Efficient discrimination of temporal patterns by motion-sensitive neurons in primate visual cortex

Although motion-sensitive neurons in macaque middle temporal (MT) area are conventionally characterized using stimuli whose velocity remains constant for 1-3 s, many ecologically relevant stimuli change on a shorter time scale (30-300 ms). We compared neuronal responses to conventional (constant-velocity) and time-varying stimuli in alert primates. The responses to both stimulus ensembles were well described as rate-modulated Poisson processes but with very high precision (approximately 3 ms) modulation functions underlying the time-varying responses. Information-theoretic analysis revealed that the responses encoded only approximately 1 bit/s about constant-velocity stimuli but up to 29 bits/s about the time-varying stimuli. Analysis of local field potentials revealed that part of the residual response variability arose from "noise" sources extrinsic to the neuron. Our results demonstrate that extrastriate neurons in alert primates can encode the fine temporal structure of visual stimuli.

D1 agonist CY208-243 attenuates the pattern electroretinogram to low spatial frequency stimuli in the monkey

We investigated whether or not the D1 agonist, CY 208-243, affects the spatial tuning function of pattern electroretinogram (PERG). Two lightly anaesthetised monkeys were studied before and after CY 208-243 or placebo administration. The results show that the PERG response to 0.5 cycles/degree (c/d; coarse), but not to 2.3 c/d (medium) spatial frequency stimuli disappears following systemic administration of this drug. Since previous results show that D2 blockers attenuate the PERG only above 2.3 c/d, foremost the peak of the normal spatial frequency response function, the current results suggest that dopamine itself, via D1 receptors, may be responsible for the low spatial frequency decline of normal spatial PERG tuning function. We infer that the synergistic activation of D1 and D2 receptors is needed to shape the spatially tuned primate ERG.

Seed dispersal by neotropical seed predators

From a plant's perspective, the difference between a seed predator and a seed disperser should be straightforward: attract animals that will disperse seeds and defend seeds from potential predators. Unlike pulp-eating frugivores, seed predators regularly encounter diverse plant protective mechanisms. The purpose of this paper is to examine feeding constraints, morphological adaptations, and the mechanical process of seed predation. While there is evidence that some seed predators cause severe losses to seed crops, there is also evidence that seed predators enhance seed dispersal and germination. We also examine four methods by which neotropical seed predators may contribute to dispersal. 1) Seed predators examined here ingested fruit when seeds were full-sized, but not yet mature (i.e., seeds of mature fruit may be avoided by seed predators and available for dispersal by other frugivores). 2) Sympatric seed predators may ingest seeds from different plants thus reducing overall predator load on any individual plant. 3) Seed predators that manipulate seeds (e.g., remove pericarp and seed coat) may enhance germination if the prepared seeds are dropped, discarded, or buried and not ingested. 4) Small seeds may miss mastication and swallowed intact with a food bolus. The last mechanism is the most likely to contribute to seed dispersal by the widest array of vertebrate seed predators, but primate seed predators may facilitate seed dispersal using all four mechanisms. Therefore, the traditional dichotomy of seed predator vs. seed disperser oversimplifies the interactions between seed predators and plants.

Mechanisms of visual object recognition: monkey and human studies

The feature-based representations of object images in the inferotemporal cortex of macaque monkeys have been further characterized by optical imaging experiments. Recently, the close correlation between the activity of inferotemporal cells and the perception of object images has been revealed by single-unit recordings from behaving monkeys. The human homologue of the monkey inferotemporal cortex has been identified through use of new non-invasive techniques.

Active emmetropization--evidence for its existence and ramifications for clinical practice

There is increasing evidence from animal studies in support of the concept of an active emmetropization mechanism which has potentially important clinical ramifications for the management of refractive errors. Recent research into refractive development and emmetropization is reviewed, with emphasis given to work involving the chick, tree shrew and monkey, which represent the three most widely used animal models in this field. The findings of this research are reviewed in a clinical context. Compensatory eye growth responses to focusing errors imposed by lenses represent the most compelling evidence for active emmetropization. These observations are complemented by other evidence showing recovery from induced refractive errors such as form-deprivation myopia. Of the animals listed above, chicks show the most impressive emmetropization, being able to compensate fully (using choroidal and scleral mechanisms) to lens powers ranging from +15 D to -10 D. The range of lens powers eliciting appropriate compensatory responses is narrower in the tree shrew and monkey, and the response patterns generally are also more complex to interpret. These data relate to young animals and together indicate refractive plasticity during development. Extrapolation of these findings to humans predicts that natural emmetropization will be inhibited in neonates by early intervention with prescription lenses, and that refractive correction of myopia will lead to accelerated progression. This convincing evidence for active emmetropization warrants due consideration in developing clinical management strategies for refractive errors.

Volumetric comparisons in the cerebellar complex of anthropoids, with special reference to locomotor types

Seven measurements in the cerebellar complex were completed on 45 individuals, including 26 species of anthropoids from Stephan's collection. These included 12 species of New World monkeys, 10 species of Old World monkeys, and Hylobates, Gorilla, Pan, and humans. The measurements were the volume of medial (fastigial) (CM), interpositus (globose and emboliform) (CI), and lateral (dentate) (CL) cerebellar nuclei, ventral pons (VPo), inferior olivary principal (OLIPr), and accessory (OLIAc) nuclei and vestibular nuclear complex (VES). The relative size of each nucleus was expressed in size indices based upon the allometric line obtained by the reduced major axis analysis. The indices of three cerebellar nuclei reflect the relative size of three longitudinal zones of the cerebellum. The cerebellar hemisphere-lateralis zone is represented by the CL indices, the vermis-medialis zone by the CM indices, and the pars intermedius-interpositus zone by the CI indices. The results show that the VPo and OLIPr indices are closely related to the CL indices. This lateral zone group of nuclei is the most progressively developed in humans, whereas the CM, CI, OLIAc, and VES are independent of the developmental trend manifest by the lateral zone group of nuclei. The indices are discussed in relation to the predominant locomotor pattern exhibited by a species. The size indices of arboreal quadrupeds show a development of all nuclei in the cerebellar complex. This is interpreted as indicating that arboreal monkeys live in complicated, discontinuous, three-dimensional space and need exceptional cerebellar capacity for each pattern of locomotion and positional behavior. Progressive development of the lateral zone group of nuclei only compared to other nuclei was recognizable in humans. This development is considered to be related not to bipedalism, but to versatile and coordinated finger movement, resulting after bipedalism was established. This cerebellar reorganization is also a prerequisite (Leiner et al. [1993] TINS 16: 444-447) for the evolution of human language. The differences between size indices of the nuclei of Macaca (= pronograde primate) and Ateles (= antipronograde one) are compared in relation to their vertical climbing kinesiological data.

Color vision of ancestral organisms of higher primates

The color vision of mammals is controlled by photosensitive proteins called opsins. Most mammals have dichromatic color vision, but hominoids and Old World (OW) monkeys enjoy trichromatic vision, having the blue-, green-, and red-sensitive opsin genes. Most New World (NW) monkeys are either dichromatic or trichromatic, depending on the sex and genotype. Trichromacy in higher primates is believed to have evolved to facilitate the detection of yellow and red fruits against dappled foliage, but the process of evolutionary change from dichromacy to trichromacy is not well understood. Using the parsimony and the newly developed Bayesian methods, we inferred the amino acid sequences of opsins of ancestral organisms of higher primates. The results suggest that the ancestors of OW and NW monkeys lacked the green gene and that the green gene later evolved from the red gene. The fact that the red/green opsin gene has survived the long nocturnal stage of mammalian evolution and that it is under strong purifying selection in organisms that live in dark environments suggests that this gene has another important function in addition to color vision, probably the control of circadian rhythms.

Anthropoid origins

Recent fossil discoveries have greatly increased our knowledge of the morphology and diversity of early Anthropoidea, the suborder to which humans belong. Phylogenetic analysis of Recent and fossil taxa supports the hypotheses that a haplorhine-strepsirrhine dichotomy existed at least at the time of the earliest record of fossil primates (earliest Eocene) and that eosimiids (middle Eocene, China) are primitive anthropoids. Functional analysis suggests that stem haplorhines were small, nocturnal, arboreal, visually oriented insectivore-frugivores with a scurrying-leaping locomotion. A change from nocturnality to diurnality was the fundamental adaptive shift that occurred at the base of the tarsier-eosimiid-anthropoid clade. Stem anthropoids remained small diurnal arborealists but adopted locomotor patterns with more arboreal quadrupedalism and less leaping. A shift to a more herbivorous diet occurred in several anthropoid lineages.

Behavioral and physiological effects of xanthines in nonhuman primates

Caffeine and related xanthines can have significant behavioral effects on measures of locomotor activity, schedule-controlled behavior, drug self-administration, and learning and memory. Xanthines also produce numerous physiological effects including positive inotropic and chronotropic effects on the heart, decreased airway resistance in the lung, and respiratory stimulation. Due to the widespread use of xanthines as constituents of food and beverages and as therapeutic drugs, identification of mechanisms that mediate their pharmacological effects has considerable relevance for drug development and therapeutics. Two primary mechanisms involving the cyclic nucleotide system have been implicated as the bases for the effects of xanthines in the CNS. Many xanthines bind to specific adenosine recognition sites and block the actions of adenosine. Xanthines also inhibit cyclic nucleotide phosphodiesterases, the enzymes responsible for the hydrolytic inactivation of cyclic AMP and cyclic GMP. Recent research in nonhuman primates has characterized the behavioral, respiratory and cardiovascular effects of a number of xanthines and related drugs differing in affinity at different subtypes of adenosine receptors and in capacity to inhibit different molecular forms of PDE. The behavioral-stimulant effects of xanthines appear to be mediated principally by their adenosine-antagonist actions and may be limited by PDE inhibition. The respiratory-stimulant and cardiac effects of xanthines, on the other hand, appear to be linked more closely to their PDE-inhibiting actions than to adenosine antagonism. Converging lines of evidence suggest that adenosine A2 and cAMP-specific (possibly type IV) PDE mechanisms play especially prominent roles in mediating the behavioral and physiological effects of xanthines in nonhuman primates.

Activity and attention in zinc-deprived adolescent monkeys

Lethargy is characteristic of malnourished populations, but little is known about the biologic mechanism or consequences for cognitive performance. In the current experiment, 24-h activity patterns and performance of an attention task were studied in adolescent female monkeys (18-33 mo of age, n = 10/group) under conditions of moderate dietary zinc deprivation (2 micrograms Zn/g diet) and adequate dietary zinc (50 micrograms Zn/g). There were progressive decreases in daytime activity levels in the zinc-deprived group followed by slowing of growth around the time of the growth spurt. Attention performance was also impaired before the onset of growth retardation. Zinc-deprived monkeys failed to show the shift to later initiation of the rest phase of the diurnal cycle seen in controls in late adolescence. These data support previous findings that activity and attention can be affected during early stages of zinc deprivation before the onset of growth retardation.

Arm movements in monkeys: behavior and neurophysiology

Reaching to objects of interest is very common in the behavioral repertoire of primates. Monkeys possess keen binocular vision and make graceful and accurate arm movements. This review focuses on behavioral and neurophysiological aspects of eye-hand coordination in behaving monkeys, including neural coding mechanisms at the single cell level and in neuronal populations. The results of these studies have converged to a common behavioral-neurophysiological ground and provided a springboard for studies of brain mechanisms underlying motor cognitive function.

The spinal cord and its brain: representations and models. To what extent do forebrain mechanisms appear at brainstem spinal cord levels?

This review takes up and updates some major issues dealt with in the book "How brain-like is the spinal cord?" (Windhorst, U. (1988) How Brain-like is the Spinal Cord? Interacting Cell Assemblies in the Nervous System. Springer: Berlin). 1. The main subject dealt with in the book was on the code used by the central nervous system (CNS) to represent and convey information. Specifically, it was proposed that, apart from the generally accepted frequency code (rate of cell firing) and others, information is also encoded in the synchronized or otherwise correlated firing of assemblies of neurons. (ii) Since the temporary establishment of cell assemblies requires mechanisms of flexible neuronal interactions, the second important topic was neuronal plasticity and memory. In fact, plasticity is at the heart of the "population code" used for representation by neuronal assemblies. 2. The third topic was loosely related to a specific representation in the CNS, namely that by so-called "internal models" that represent aspects of the CNS' peripheral environment. 3. It was argued that the above mechanisms of representation and operation are used not only by higher, e.g. cortical, CNS structures, but also by the spinal cord. These topics are here dealt with in turn, always with regard to the special question as to what extent forebrain mechanisms appear at brainstem and spinal cord levels. There is accumulating evidence that in fact the spinal cord uses ensemble processing, synaptic plasticity and internal models to represent and handle its external environment.

Temporal coding in vision: coding by the spike arrival times leads to oscillations in the case of moving targets

The 'oscillations' which have been observed in the visual cortex of cats and monkeys in the case of moving targets are discussed in relation to a temporal coding based on the arrival times of spikes or bursts. A decoding process for this temporal coding is proposed in which neurons work in a correlator mode. In the case of motion analysis, periodic resetting is needed to avoid information jamming. This resetting is proposed to be responsible for the 'oscillations'. Good initial synchronization is required for the decoding process to be performed efficiently. A diffusive process based on interdendritic ionic currents is proposed and shown to operate efficiently, without any loss of spatial and temporal resolving powers.

Preliminary examination of non-occlusal dental microwear in anthropoids: implications for the study of fossil primates

Most studies of microscopic wear on non-human primate teeth have focused on the occlusal surfaces of molars. Recent analyses of the buccal surfaces of human cheek teeth have demonstrated an association between diet and dental microwear on the these surfaces as well. In the current study, we examine microwear on both the buccal and lingual surfaces of non-human primate molars to assess the potential of these surfaces to reveal information concerning anthropoid feeding behaviors. We compare frequency of microwear occurrence in 12 extant and 11 fossil anthropoid species. Among the living primates, the occurrence of microwear on nonocclusal surfaces appears to relate to both diet and degree of terrestriality. The implications of this research for the inference of feeding behaviors and substrate use in fossil cercopithecoids are discussed.