Development of the ability to detect visual motion in infant macaque monkeys

Bilateral cataract surgery in a Japanese macaque (Macaca fuscata): A case report

A 7.5-year-old intact male Japanese macaque was presented for evaluation of vision loss. After a complete ophthalmic examination, the patient was diagnosed with hypermature cataract in both eyes. After the cataract surgery, it was able to locate food and walk in a straight line.

Early Developmental Trajectories of Functional Connectivity Along the Visual Pathways in Rhesus Monkeys

Early social interactions shape the development of social behavior, although the critical periods or the underlying neurodevelopmental processes are not completely understood. Here, we studied the developmental changes in neural pathways underlying visual social engagement in the translational rhesus monkey model. Changes in functional connectivity (FC) along the ventral object and motion pathways and the dorsal attention/visuo-spatial pathways were studied longitudinally using resting-state functional MRI in infant rhesus monkeys, from birth through early weaning (3 months), given the socioemotional changes experienced during this period. Our results revealed that (1) maturation along the visual pathways proceeds in a caudo-rostral progression with primary visual areas (V1-V3) showing strong FC as early as 2 weeks of age, whereas higher-order visual and attentional areas (e.g., MT-AST, LIP-FEF) show weak FC; (2) functional changes were pathway-specific (e.g., robust FC increases detected in the most anterior aspect of the object pathway (TE-AMY), but FC remained weak in the other pathways (e.g., AST-AMY)); (3) FC matures similarly in both right and left hemispheres. Our findings suggest that visual pathways in infant macaques undergo selective remodeling during the first 3 months of life, likely regulated by early social interactions and supporting the transition to independence from the mother.

Visual development in primates: Neural mechanisms and critical periods

Despite many decades of research into the development of visual cortex, it remains unclear what neural processes set limitations on the development of visual function and define its vulnerability to abnormal visual experience. This selected review examines the development of visual function and its neural correlates, and highlights the fact that in most cases receptive field properties of infant neurons are substantially more mature than infant visual function. One exception is temporal resolution, which can be accounted for by resolution of neurons at the level of the lateral geniculate nucleus (LGN). In terms of spatial vision, properties of single neurons alone are not sufficient to account for visual development. Different visual functions develop over different time courses. Their onset may be limited by the existence of neural response properties that support a given perceptual ability, but the subsequent time course of maturation to adult levels remains unexplained. Several examples are offered suggesting that taking account of weak signaling by infant neurons, correlated firing, and pooled responses of populations of neurons brings us closer to an understanding of the relationship between neural and behavioral development.

Fast development of global motion processing in human infants

Although global motion processing is thought to emerge early in infancy, there is debate regarding the age at which it matures to an adult-like level. In the current study, we address the possibility that the apparent age-related improvement in global motion processing might be secondary to age-related increases in the sensitivity of mechanisms (i.e., local motion detectors) that provide input to global motion mechanisms. To address this, we measured global motion processing by obtaining motion coherence thresholds using stimuli that were equally detectable in terms of contrast across all individuals and ages (3-, 4-, 5-, 6-, and 7-month-olds and adults). For infants, we employed a directional eye movement (DEM) technique. For adults, we employed both DEM and a self-report method. First, contrast sensitivity was obtained for a local task, using a stochastic motion display in which all the dots moved coherently. Contrast sensitivity increased significantly between 3 and 7 months, and between infancy and adulthood. Each subject was then tested on the global motion task with the contrast of the dots set to 2.5 × each individual's contrast threshold. Coherence thresholds were obtained by varying the percentage of coherently moving "signal" versus "noise" dots in the stochastic motion display. Results revealed remarkably stable global motion sensitivity between 3 and 7 months of age, as well as between infancy and adulthood. These results suggest that the mechanisms underlying global motion processing develop to an adult-like state very quickly.

Normal development of pattern motion sensitivity in macaque monkeys

We studied the development of sensitivity to complex motion using plaid patterns. We hypothesized, based on neurophysiological data showing a dearth of pattern direction-selective (PDS) cells in area medial temporal (MT) of infant macaques, that sensitivity to pattern motion would develop later than other forms of global motion sensitivity. We tested 10 macaque monkeys (Macaca nemestrina) ranging in age from 7 weeks to 109-160 weeks (adult). The monkeys discriminated horizontal from vertical pattern motion; sensitivity for one-dimensional (1D) direction discrimination and detection were tested as control tasks. The results show that pattern motion discrimination ability develops relatively late, between 10 and 18 weeks, while performance on the 1D control tasks was excellent at the earliest test ages. Plaid discrimination performance depends on both the speed and spatial scale of the underlying patterns. However, development is not limited by contrast sensitivity. These results support the idea that pattern motion perception depends on a different mechanism than other forms of global motion perception and are consistent with the idea that the representation of PDS neurons in MT may limit the development of complex motion perception.

Development of sensitivity to visual motion in macaque monkeys

The development of spatial vision is relatively well documented in human and nonhuman primates. However, little is known about the development of sensitivity to motion. We measured the development of sensitivity to direction of motion, and the relationship between motion and contrast sensitivity in macaque monkeys as a function of age. Monkeys (Macaca nemestrina, aged between 10 days and 3 years) discriminated direction of motion in random-dot kinematograms. The youngest monkeys showed directionally selective orienting and the ability to integrate motion signals at large dot displacements and fast speeds. With age, coherence sensitivity improved for all spatial and temporal dot displacements tested. The temporal interval between the dots was far less important than the spatial offset in determining the animals' performance at all but the youngest ages. Motion sensitivity improved well beyond the end of the first postnatal year, when mid-spatial-frequency contrast sensitivity reached asymptote, and continued for at least 3 years. Sensitivity to contrast at high spatial frequencies also continued to develop beyond the end of the first year. We conclude that the development of motion sensitivity depends on mechanisms beyond the low-level filters presumed to limit acuity and contrast sensitivity, and most likely reflects the function of extrastriate visual areas.

Postnatal development of alkaline phosphatase activity correlates with the maturation of neurotransmission in the cerebral cortex

We have shown previously that the tissue nonspecific alkaline phosphatase (TNAP) is selectively expressed in the synaptic cleft of sensory cortical areas in adult mammals and, by using sensory deprivation, that TNAP activity depends on thalamocortical activity. We further analyzed this structural functional relationship by comparing the developmental pattern of TNAP activity to the maturation of the thalamocortical afferents in the primate brain (Callithrix jacchus). Cortical expression of alkaline phosphatase (AP) activity reflects the sequential maturation of the modality-specific sensory areas. Within the visual cortex, the regional and laminar distribution of AP correlates with the differential maturation of the magno- and parvocellular streams. AP activity, which is transiently expressed in the white matter, exhibits a complementary distributional pattern with myelin staining. Ultrastructural analysis revealed that AP activity is localized exclusively to the myelin-free axonal segments, including the node of Ranvier. It was also found that AP activity is gradually expressed in parallel with the maturation of synaptic contacts in the neuropile. These data suggest the involvement of AP, in addition to neurotransmitter synthesis previously suggested in the adult, in synaptic stabilization and in myelin pattern formation and put forward a role of AP in cortical plasticity and brain disorders.

Topographic and Laminar Maturation of Striate Cortex in Early Postnatal Marmoset Monkeys, as Revealed by Neurofilament Immunohistochemistry

The maturation of pyramidal neurons in the primary visual cortex (V1) of marmoset monkeys was investigated using an antibody (SMI-32) to non-phosphorylated neurofilament protein (NNF). Analysis of animals aged between birth and postnatal day 91 (PD 91, which corresponds approximately to the peak of synaptogenesis in this species) revealed discrete changes in both the laminar and the areal distribution of NNF. At PD 0, the upper part of layer 6 contained darkly labelled neurons and associated neuropil, including axons. In this layer a centroperipheral gradient, with more labelled cells in the foveal representation, was apparent at PD 0. This topographic gradient gradually disappeared, and by PD 91 a similar density of labelled layer 6 cells was observed throughout V1. Labelled cells were not apparent in layer 3C until PD 7, and were not distributed according to a topographic gradient. Labelled cells were first observed in layer 3B(alpha) at PD 28, when they formed a centroperipheral gradient similar to that seen in layer 6. This gradient was still evident in an adult animal. These results demonstrate an inside-out profile of postnatal cortical development, with the topographic pattern of maturation of V1 mimicking the centroperipheral gradient of maturation in the retina.

Vascularization in the primate visual cortex during development

We studied the relationship between vascularization and neuronal activity in the visual cortex during postnatal development in the primate. Analyses were focused on layer IVC that displays a sequential pattern of maturation for the magno- and parvocellular systems in separate sublayers, respectively IVC alpha and IVC beta. Cytochrome oxidase and endogenous alkaline phosphatase histochemistry was used to analyse, on the same sections, the laminar patterns of cortical activity and vessel density in the primary visual cortex of the marmoset (Callithrix jacchus). Experiments were carried out in five young and two adult animals. We showed that the temporal pattern of angiogenesis differs in layer IVC alpha and IVC beta. During the first postnatal month, vessel density is higher in IVC alpha than in IVC beta and runs parallel to cytochrome oxidase intensity. In 2-month-old animals, both vessel densities and cytochrome oxidase activity are similar in IVC alpha and IVC beta. In adults, the vessel densities in IVC alpha and IVC beta are the reverse of those observed during the first postnatal month. Vessel diameter does not account for this evolution in vascular patterns. In the discussion, we suggest that such a developmental time-course of angiogenesis might be linked to the synaptogenesis requirements that proceed differently for the magno- and parvocellular systems in the primate striate cortex.

Development of the optokinetic system in macaque monkeys

Optokinetic nystagmus in response to horizontal movement of a whole field random dot pattern was measured in infant macaque monkeys from the first week to about 5 months after birth using electrooculography. During monocular and binocular viewing conditions stimulus velocities were varied between 10 and 120 degrees/s. Monocular stimulation in the temporonasal direction yielded slow phase gain of the optokinetic system which was relatively constant for a given stimulus velocity over the whole period of observation. Gain during nasotemporal stimulation was also clearly present but significantly lower at early stages and increased during further development. This asymmetry of monocular horizontal optokinetic nystagmus (OKN) clearly depended on the stimulus velocity. At lower stimulus velocities (10-20 degrees/s) OKN was largely symmetrical at 2-5 weeks of age. At higher stimulus velocities (40 degrees/s) symmetry was reached at about 12 weeks of age or even much later (80-120 degrees/s).

Infants' sensitivity to uniform motion

Uniform motion across the retina is a powerful cue to the perception of self-motion. In spite of its importance for adaptive functioning, little is known about the early development of uniform motion sensitivity. Six-, 12-, and 18-week-old infants viewed random-dot kinematograms depicting leftward or rightward uniform motion. The display induced optokinetic nystagmus (OKN), which a trained observer used to judge the direction of target motion. Both speed of motion and directional coherence were varied to obtain independent motion detection thresholds. Infants of all three ages could detect uniform motion, and their detection thresholds were constant during this period of development. This is in contrast to the clear improvements in relative motion sensitivity noted previously between 6 and 18 weeks of age with a preferential looking (PL) paradigm. The developmental differences between these studies may result from: (1) separate mechanisms for detecting uniform (absolute) and differential (relative) motion; or (2) separate mechanisms underlying OKN and PL response measures.

Learning of a hiding task and a delayed response task in infant rhesus monkeys

The ability of the prefrontal cortex to learn was studied in 2-4-month-old male rhesus monkeys. Either the classical Delayed Response task with an opaque screen during the delay period or a Delayed Response task without a screen (the 'Hiding task') were performed every day beginning when the monkeys were 2 months old. The criterion for having learned the task was a correct performance rate of > 80% for two consecutive days. The Hiding task with a 0-s delay, training of which began at 50 days, was learned at 67 days. When the monkeys had reached 4 months of age, they were able to perform the Delayed Response task with a 3-s delay. During learning when the performance rate was low, monkeys tended to make perseverative errors, and tended to select the target position erroneously that was ipsilateral to the hand used. The rate of perseveration errors decreased linearly as the performance rate increased. Thus, 2-4-months-old monkeys in which synapses are produced in great abundance in the cortex, were capable of learning a Delayed Response task with a 3-s delay.