Development of sensitivity to visual texture modulation in macaque monkeys

Development of radial frequency pattern perception in macaque monkeys

Infant primates see poorly, and most perceptual functions mature steadily beyond early infancy. Behavioral studies on human and macaque infants show that global form perception, as measured by the ability to integrate contour information into a coherent percept, improves dramatically throughout the first several years after birth. However, it is unknown when sensitivity to curvature and shape emerges in early life or how it develops. We studied the development of shape sensitivity in 18 macaques, aged 2 months to 10 years. Using radial frequency stimuli, circular targets whose radii are modulated sinusoidally, we tested monkeys' ability to radial frequency stimuli from circles as a function of the depth and frequency of sinusoidal modulation. We implemented a new four-choice oddity task and compared the resulting data with that from a traditional two-alternative forced choice task. We found that radial frequency pattern perception was measurable at the youngest age tested (2 months). Behavioral performance at all radial frequencies improved with age. Performance was better for higher radial frequencies, suggesting the developing visual system prioritizes processing of fine visual details that are ecologically relevant. By using two complementary methods, we were able to capture a comprehensive developmental trajectory for shape perception.

An Automated Visual Psychophysics Method to Measure Visual Function in Swine Preclinical Animal Model

Purpose

The aim of this study was to develop and validate a test to assess visual function in pigs using the visual psychophysics contrast sensitivity function.

Methods

We utilized a touchscreen along with a pellet reward dispenser to train three Göttingen pigs on a visual psychophysics test and determined their contrast sensitivity function. Images with different contrast resolutions were used as visual stimuli and presented against a control image in a two-choice test. Following animals' acclimatization and the first phase of training, the system was arranged such that animals could self-run multiple consecutive trials without human intervention.

Results

All animals were trained within a week and remembered the task with 1 day of reinforcement when tested 1 month after the last visual assessment. All trained animals performed well during the trial with minimal screen side bias, especially at contrast threshold above 40%.

Conclusions

Göttingen pigs are trainable for a visual psychophysics test and able to self-run the trial without human intervention.

Translational Relevance

Contrast sensitivity is one of the key parameters to assess visual function in humans. The possibility of measuring the same parameters in a large animal model allows for a better translation and understanding of drug safety and efficacy in preclinical ophthalmology.

Developmental Changes in Pyramidal Cell Morphology in Multiple Visual Cortical Areas Using Cluster Analysis

Neuronal morphology is characterized by salient features such as complex axonal and dendritic arbors. In the mammalian brain, variations in dendritic morphology among cell classes, brain regions, and animal species are thought to underlie known differences in neuronal function. In this work, we obtained a large dataset from http://neuromorpho.org/ comprising layer III pyramidal cells in different cortical areas of the ventral visual pathway (V1, V2, V4, TEO, and TE) of the macaque monkey at different developmental stages. We performed an in depth quantitative analysis of pyramidal cell morphology throughout development in an effort to determine which aspects mature early in development and which features require a protracted period of maturation. We were also interested in establishing if developmental changes in morphological features occur simultaneously or hierarchically in multiple visual cortical areas. We addressed these questions by performing principal component analysis (PCA) and hierarchical clustering analysis on relevant morphological features. Our analysis indicates that the maturation of pyramidal cell morphology is largely based on early development of topological features in most visual cortical areas. Moreover, the maturation of pyramidal cell morphology in V1, V2, V4, TEO, and TE is characterized by unique developmental trajectories.

Postnatal Development of Visual Cortical Function in the Mammalian Brain

This review aims to discuss (1) the refinement of mammalian visual cortical circuits and the maturation of visual functions they subserve in primary visual cortex (V1) and other visual cortical areas, and (2) existing evidence supporting the notion of differential rates of maturation of visual functions in different species. It is well known that different visual functions and their underlying circuitry mature and attain adultlike characteristics at different stages in postnatal development with varying growth rates. The developmental timecourse and duration of refinement varies significantly both in V1 of various species and among different visual cortical areas; while basic visual functions like spatial acuity mature earlier requiring less time, higher form perception such as contour integration is more complex and requires longer postnatal time to refine. This review will highlight the importance of systematic comparative analysis of the differential rates of refinement of visual circuitry and function as that may help reveal underlying key mechanisms necessary for healthy visual development during infancy and adulthood. This type of approach will help future studies to establish direct links between various developmental aspects of different visual cortical areas in both human and animal models; thus enhancing our understanding of vision related neurological disorders and their potential therapeutic remedies.

Development of visual cortical function in infant macaques: A BOLD fMRI study

Functional brain development is not well understood. In the visual system, neurophysiological studies in nonhuman primates show quite mature neuronal properties near birth although visual function is itself quite immature and continues to develop over many months or years after birth. Our goal was to assess the relative development of two main visual processing streams, dorsal and ventral, using BOLD fMRI in an attempt to understand the global mechanisms that support the maturation of visual behavior. Seven infant macaque monkeys (Macaca mulatta) were repeatedly scanned, while anesthetized, over an age range of 102 to 1431 days. Large rotating checkerboard stimuli induced BOLD activation in visual cortices at early ages. Additionally we used static and dynamic Glass pattern stimuli to probe BOLD responses in primary visual cortex and two extrastriate areas: V4 and MT-V5. The resulting activations were analyzed with standard GLM and multivoxel pattern analysis (MVPA) approaches. We analyzed three contrasts: Glass pattern present/absent, static/dynamic Glass pattern presentation, and structured/random Glass pattern form. For both GLM and MVPA approaches, robust coherent BOLD activation appeared relatively late in comparison to the maturation of known neuronal properties and the development of behavioral sensitivity to Glass patterns. Robust differential activity to Glass pattern present/absent and dynamic/static stimulus presentation appeared first in V1, followed by V4 and MT-V5 at older ages; there was no reliable distinction between the two extrastriate areas. A similar pattern of results was obtained with the two analysis methods, although MVPA analysis showed reliable differential responses emerging at later ages than GLM. Although BOLD responses to large visual stimuli are detectable, our results with more refined stimuli indicate that global BOLD activity changes as behavioral performance matures. This reflects an hierarchical development of the visual pathways. Since fMRI BOLD reflects neural activity on a population level, our results indicate that, although individual neurons might be adult-like, a longer maturation process takes place on a population level.

Age norms for grating acuity and contrast sensitivity measured by Lea tests in the first three years of life

AIM

To determine age norms in the first three years of life for grating visual acuity and contrast sensitivity obtained with Lea grating test and Hiding Heidi low contrast face test.

METHODS

Lea grating test was used to estimate binocular grating acuity and Hiding Heidi low contrast face test was used to estimate contrast sensitivity in 600 healthy infants and children. Age ranged from 3 to 36mo subdivided into 12 groups subjected for full ophthalmologic and pediatric examinations.

RESULTS

The grating acuity developed along the first three years of life. It ranged from 1.88±0.32 c/d at 3mo to 30.95±0.77 c/d at 36mo. The most rapid development was during the first 12mo and the slowest development was from 30 to 36mo. The contrast sensitivity showed rapid development in the first two years of life. Its mean value ranged from 4.23±1.17 at 3mo to 78.26±8.21 at 24mo. It was constant at the highest score (80) thereafter.

CONCLUSION

Age norms for grating acuity along with contrast sensitivity offer a more comprehensive measure of spatial vision and should be incorporated in clinical practice for better visual assessment in preverbal and nonverbal children.

Neural plasticity following lesions of the primate occipital lobe: The marmoset as an animal model for studies of blindsight

For nearly a century it has been observed that some residual visually guided behavior can persist after damage to the primary visual cortex (V1) in primates. The age at which damage to V1 occurs leads to different outcomes, with V1 lesions in infancy allowing better preservation of visual faculties in comparison with those incurred in adulthood. While adult V1 lesions may still allow retention of some limited visual abilities, these are subconscious-a characteristic that has led to this form of residual vision being referred to as blindsight. The neural basis of blindsight has been of great interest to the neuroscience community, with particular focus on understanding the contributions of the different subcortical pathways and cortical areas that may underlie this phenomenon. More recently, research has started to address which forms of neural plasticity occur following V1 lesions at different ages, including work using marmoset monkeys. The relatively rapid postnatal development of this species, allied to the lissencephalic brains and well-characterized visual cortex provide significant technical advantages, which allow controlled experiments exploring visual function in the absence of V1. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 314-327, 2017.

A Window into brain development: hdEEG methods to track visual development in nonhuman primates

Electroencephalography (EEG) is widely used to study human brain activity, and is a useful tool for bridging the gap between invasive neural recording assays and behavioral data. High-density EEG (hdEEG) methods currently used for human subjects for use with infant macaque monkeys, a species that exhibits similar visual development to humans over a shorter time course was adapted. Unlike monkeys, human subjects were difficult to study longitudinally and were not appropriate for direct within-species comparison to neuronal data. About 27-channel electrode caps, which allowed collection of hdEEG data from infant monkeys across development were designed. Acuity and contrast sweep VEP responses to grating stimuli was obtained and a new method for objective threshold estimation based on response signal-to-noise ratios at different stimulus levels was established. The developmental trajectories of VEP-measured contrast sensitivity and acuity to previously collected behavioral and neuronal data were compared. The VEP measures showed similar rates of development to behavioral measures, both of which were slower than direct neuronal measures; VEP thresholds were higher than other measures. This is the first usage of non-invasive technology in non-human primates. Other means to assess neural sensitivity in infants were all invasive. Use of hdEEG with infant monkeys opens many possibilities for tracking development of vision and other functions in non-human primates, and can expand our understanding of the relationship between neuronal activity and behavioral capabilities across various sensory and cognitive domains. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1342-1359, 2016.

Pyramidal cell development: postnatal spinogenesis, dendritic growth, axon growth, and electrophysiology

Here we review recent findings related to postnatal spinogenesis, dendritic and axon growth, pruning and electrophysiology of neocortical pyramidal cells in the developing primate brain. Pyramidal cells in sensory, association and executive cortex grow dendrites, spines and axons at different rates, and vary in the degree of pruning. Of particular note is the fact that pyramidal cells in primary visual area (V1) prune more spines than they grow during postnatal development, whereas those in inferotemporal (TEO and TE) and granular prefrontal cortex (gPFC; Brodmann's area 12) grow more than they prune. Moreover, pyramidal cells in TEO, TE and the gPFC continue to grow larger dendritic territories from birth into adulthood, replete with spines, whereas those in V1 become smaller during this time. The developmental profile of intrinsic axons also varies between cortical areas: those in V1, for example, undergo an early proliferation followed by pruning and local consolidation into adulthood, whereas those in area TE tend to establish their territory and consolidate it into adulthood with little pruning. We correlate the anatomical findings with the electrophysiological properties of cells in the different cortical areas, including membrane time constant, depolarizing sag, duration of individual action potentials, and spike-frequency adaptation. All of the electrophysiological variables ramped up before 7 months of age in V1, but continued to ramp up over a protracted period of time in area TE. These data suggest that the anatomical and electrophysiological profiles of pyramidal cells vary among cortical areas at birth, and continue to diverge into adulthood. Moreover, the data reveal that the “use it or lose it” notion of synaptic reinforcement may speak to only part of the story, “use it but you still might lose it” may be just as prevalent in the cerebral cortex.

Linking structure and function: development of lateral spatial interactions in macaque monkeys

Lateral spatial interactions among elements of a scene, which either enhance or degrade visual performance, are ubiquitous in vision. The neural mechanisms underlying lateral spatial interactions are a matter of debate, and various hypotheses have been proposed. Suppressive effects may be due to local inhibitory interactions, whereas facilitatory effects are typically ascribed either to the function of long-range horizontal projections in V1 or to uncertainty reduction. We investigated the development of lateral spatial interactions, facilitation and suppression, and compared their developmental profiles to those of potential underlying mechanisms in the visual system of infant macaques. Animals ranging in age from 10 weeks to 3 years were tested with a lateral masking paradigm. We found that suppressive interactions are present from very early in postnatal life, showing no change over the age range tested. However, facilitation develops slowly over the first year after birth. Our data suggest that the early maturation of suppressive interactions is related to the relatively mature receptive field properties of neurons in early visual cortical areas near birth in infant macaques, whereas the later maturation of facilitation is unlikely to be explained by development of local or long-range connectivity in primary visual cortex. Instead our data favor a late developing feedback or top-down cognitive process to explain the origin of facilitation.

Receptive-field subfields of V2 neurons in macaque monkeys are adult-like near birth

Infant primates can discriminate texture-defined form despite their relatively low visual acuity. The neuronal mechanisms underlying this remarkable visual capacity of infants have not been studied in nonhuman primates. Since many V2 neurons in adult monkeys can extract the local features in complex stimuli that are required for form vision, we used two-dimensional dynamic noise stimuli and local spectral reverse correlation to measure whether the spatial map of receptive-field subfields in individual V2 neurons is sufficiently mature near birth to capture local features. As in adults, most V2 neurons in 4-week-old monkeys showed a relatively high degree of homogeneity in the spatial matrix of facilitatory subfields. However, ∼25% of V2 neurons had the subfield map where the neighboring facilitatory subfields substantially differed in their preferred orientations and spatial frequencies. Over 80% of V2 neurons in both infants and adults had "tuned" suppressive profiles in their subfield maps that could alter the tuning properties of facilitatory profiles. The differences in the preferred orientations between facilitatory and suppressive profiles were relatively large but extended over a broad range. Response immaturities in infants were mild; the overall strength of facilitatory subfield responses was lower than that in adults, and the optimal correlation delay ("latency") was longer in 4-week-old infants. These results suggest that as early as 4 weeks of age, the spatial receptive-field structure of V2 neurons is as complex as in adults and the ability of V2 neurons to compare local features of neighboring stimulus elements is nearly adult like.

Development of sensitivity to global form and motion in macaque monkeys (Macaca nemestrina)

To explore the relative development of the dorsal and ventral extrastriate processing streams, we studied the development of sensitivity to form and motion in macaque monkeys (Macaca nemestrina). We used Glass patterns and random dot kinematograms (RDK) to assay ventral and dorsal stream function, respectively. We tested 24 animals, longitudinally or cross-sectionally, between the ages of 5 weeks and 3 years. Each animal was tested with Glass patterns and RDK stimuli with each of two pattern types--circular and linear--at each age using a two alternative forced-choice task. We measured coherence threshold for discrimination of the global form or motion pattern from an incoherent control stimulus. Sensitivity to global motion appeared earlier than to global form and was higher at all ages, but performance approached adult levels at similar ages. Infants were most sensitive to large spatial scale (Δx) and fast speeds; sensitivity to fine scale and slow speeds developed more slowly independently of pattern type. Within the motion domain, pattern type had little effect on overall performance. However, within the form domain, sensitivity for linear Glass patterns was substantially poorer than that for concentric patterns. Our data show comparatively early onset for global motion integration ability, perhaps reflecting early development of the dorsal stream. However, both pathways mature over long time courses reaching adult levels between 2 and 3 years after birth.