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This chapter presents a series of diagrams of rostral to caudal coronal sections of the brain of a rhesus monkey that illustrate in a composite manner the association, commissural, projection, and striatal fiber bundles. The fiber bundles are outlined on the coronal sections, and the fibers traveling within the bundles are color-coded according to the lobe in which they originate.

This chapter presents the photomicrographs of the medial, lateral, and basal surfaces of the rhesus monkey cerebral hemisphere that researchers used as the template brain, to show the various sulci. Diagrams representing the medial, lateral, and basal surfaces of the cerebral hemisphere show the various architectonic areas, and photomicrographs of coronal sections of the template brain taken at the levels depicted on the lateral surface of the hemisphere are also shown. The chapter outlines the trajectories in the coronal plane of the various fiber pathways in the experimental cases 1 through 36 and all the summary diagrams correspond to the images shown in these photomicrographs. The photomicrographs also designate the location of the sulci and demarcate the borders of the architectonic areas referred to throughout this book.

Studies have been conducted on the rhesus monkey to determine what happens to the central nervous system (CNS) during normal aging. This chapter focuses one age-related change—the profound alterations in myelinated nerve fibers of the CNS. It shows that although there is a strong correlation between nerve fiber loss and age in the white matter tracts, only nerve fiber loss from the anterior commissure and the fornix showed correlations with cognitive decline; fiber loss from the splenium of the corpus callosum did not. The frequency of degenerative alterations in myelin sheaths correlates strongly with age, and as well with cognitive decline. Because myelin provides insulation around nerve fibers and makes saltatory conduction possible, it seems likely that any degenerative alterations in myelin sheaths will affect impulse conduction, as would an interposition of a number of short internodal lengths that occur in remyelination.

This chapter presents findings from studies of defensive behaviors in Rhesus monkeys which are relevant to understanding fear and anxiety-related psychopathology in humans. The physiological component of these fear-related behaviors is examined to reveal the causal factors of individual differences in fearful temperament. These studies complement the basic work on rodents discussed in prior chapters. Rhesus monkeys were chosen as subjects for the experiments since they share key biological and social characteristics with humans and have shorter life spans that enable longitudinal studies. This chapter discusses the laboratory paradigm developed to characterize fearful behavioral responses in the subjects and to identify which animals have fearful and anxious dispositions. The studies presented also yield relevant findings on the development of defensive responses — its neuropharmacological regulation and physiological components. The findings cited deficiencies in the regulation of adaptive emotional and defensive behavioral responses as the causes of anxiety-related psychopathology.

This chapter discusses the results of the investigation of the extreme capsule (EmC) of rhesus monkey brains. It shows that the EmC is the principal association pathway linking the middle superior temporal region with the caudal parts of the orbital cortex and the ventral-lateral prefrontal cortex. In addition to carrying these long association fiber connections, the fibers destined for the claustrum from the parietal, temporal, and frontal lobes also traverse the EmC.

This chapter discusses the results of the investigation of the middle longitudinal fasciculus (MdLF) of rhesus monkey brains. Observations confirm the presence of the MdLF pathway that lies in the white matter of the superior temporal gyrus (STG) and extends from the caudal end of the STG to the temporal pole. In addition to the fibers within the MdLF that arise in the caudal inferior parietal lobule and terminate in the STG and the cortex of the superior temporal sulcus, researchers observed that the MdLF conveys fibers from the caudal cingulated gyrus and the middle sector of the parahippocampal gyrus toward the multimodal cortex (area TPO and PGa) in the upper bank of the superior temporal sulcus. Further, the MdLF links caudal with rostral sectors within the superior temporal region itself. In addition, fibers arise from the lateral and orbital prefrontal cortices and travel caudally first in the extreme capsule, and then within the MdLF to terminate in area TPO.

This chapter discusses three aspects of visual perception in nonhuman primates (rhesus monkeys and chimpanzees) and birds (pigeons). The first is the Ponzo illusion — we perceive the object located near the apex of the inverted V to be larger than that located farther from the apex. The second is amodal completion — we complete the portion of a figure that is partly occluded by another to perceive an intact figure. The third is spatiotemporal boundary formation — we perceive a boundary of a figure that is never explicitly presented from fragmentary information. This chapter also examines the perception of object unity in nonhuman primates.

This chapter begins with historical accounts of the anterior commissure (AC). It then discusses the results of the investigation of the AC of rhesus monkey brains. It shows that the AC traverses the midline as a compact and prominent fiber bundle located immediately in front of the anterior columns of the fornix, situated above the basal forebrain and beneath the medial and ventral aspect of the anterior limb of the internal capsule. In the hemisphere it moves caudally and passes laterally through the ventral aspect of the globus pallidus. It continues laterally beneath the putamen and descends lateral to the amygdala into the temporal stem. Further caudally, the AC is located lateral to the ventral aspect of the putamen and the tail of the caudate nucleus and medial to the ventral aspect of the claustrum.

In addition to the corpus callosum and anterior commissure, there are three other fiber systems that link the ventral limbic and paralimbic regions across the hemispheres. In the present study, only Case 13 showed fibers in one of these commissures. This chapter focuses on hippocampal commissures. It theorizes that their role may be related, at least in part, to declarative learning and memory, which have been shown to depend on the integrity of structures in the medial temporal lobe that are linked by these commissures.

This chapter explores vestibulo-ocular reflex, which generates eye movements during active or passive head motion. Ideally, the eyes should move with an equal velocity as the head, but in the opposite direction. This leads to perfect gaze stabilization. The chapter specifically examines to what extent directions of stimulus and eye rotations are collinear. The specific question of whether the rotation axes of the angular acceleration stimulus and the eye rotation coincide, or whether conditions can be found where they diverge, is explored. With the rotation axis earth-vertical, labyrinthine input is restricted to activity arising in hair cells of semicircular canals. When animals are rotated in the light, the combination of vestibular together with pursuit and optokinetic input leads to even more complex interactions between reflex responses and Listing's law. Optokinetic nystagmus shows a similar anisotropy, which, like vestibular nystagmus, is further influenced by the direction of gravity. It remains to be explored whether these anisotropies can be reduced to the same neuronal mechanisms, or whether they develop and are maintained independently from each other.

This chapter outlines the different methods used to study the association, commissural, and projection of fiber pathways in the rhesus monkey brain. Topics discussed include autoradiography, the Nissl-stained template brain, cytoarchitecture of rhesus brains, the rationale for use of a standard template for brain selection of template brain sections, and photomicrography.

This chapter presents a paper entitled “Spatial and Chromatic Interactions in the Lateral Geniculate Body of the Rhesus Monkey”. This paper represents the first effort in mammalian visual neurophysiology to examine the color sensitivities of the different spatial subdivisions of receptive fields. The study examined in detail how cells respond to variations in stimulus, size, shape, and wavelength. It explored the connections of rods and cones with single fourth-order cells by working in various states of light and dark adaptation. A wide variety of cell types were found to be present in the monkey geniculate. Some were concerned mainly with spatial variables, others with color, but most were able to handle both variables.

This chapter discusses the results of the investigation of the cingulum bundle (CB) of rhesus monkey brains. The observations regarding the location and course of the CB are in general agreement with the conclusions of earlier investigators. The CB stretches from the frontal lobe around the rostrum and genu of the corpus callosum, extends caudally above the corpus callosum lateral to the cingulate gyrus, curves ventrally around the splenium, and then lies in the white matter of the ventral part of the temporal lobe— the parahippocampal gyrus. The confusing nomenclature used to designate the various components of the CB appears to be a result of the complexity of the white matter tracts conveyed within and through it. The CB may be conceptualized in the same manner as the white matter underlying any other cortical region in that it conveys long association, short association, striatal, subcortical (including thalamic and pontine), and commissural fibers.

This chapter begins with historical accounts of the corpus callosum (CC). It then discusses the results of the investigation of the CC of rhesus monkey brains. Fibers destined to traverse the CC and travel to the opposite hemisphere leave the cortex of any given cortical area as part of the dense cord of fibers lying in the central part of the white matter. Callosal fibers are sometimes identifiable as distinct from the subcortical bundle that forms the other major component of the cord, but more usually they are indistinguishable from them early in their course. As the cord fibers leave the white matter of the gyrus, they separate into two major components—the commissural fibers course medially to enter the CC, and the subcortical fibers take a course unique to each cortical area. Callosal fibers from the different parts of the cerebral cortex gather above and lateral to the lateral ventricle, enter the CC, and course medially in a compact bundle in a topographical manner to reach the opposite hemisphere.

This chapter begins with a historical overview of two systems: the true inferior longitudinal fasciculus (ILF) and the sagittal stratum. It then discusses the results of the investigation of the ILF of rhesus monkey brains. Among these is the observation that the ILF is a long association fiber system that runs in the white matter of the parietal, occipital, and temporal lobes. It is the preeminent fiber tract that conveys information in a bidirectional manner between the occipital lobe (preoccipital gyrus) and the temporal lobe.

This chapter begins with a historical account of the study of the saggital stratum (SS). It then discusses the results of the investigation of the SS of rhesus monkey brains. The SS is a major corticosubcortical white matter bundle that conveys fibers from the parietal, occipital, cingulate, and temporal regions to subcortical destinations in the thalamus, the nuclei of the basis pontis, and other brainstem structures. It also conveys afferents principally from the thalamus to the cortex. It may therefore be viewed as equivalent to the internal capsule in that it is a major subcortical fiber system and not exclusively a fiber tract linking the lateral geniculate nucleus with the calcarine cortex.

This chapter begins with a historical account of the study of the internal capsule. It then discusses the results of the investigation of the internal capsule of rhesus monkey brains. Topics covered include the anterior limb of the internal capsule, genu of the internal capsule, posterior limb of the internal capsule, internal capsule fibers from the posterior parietal cortex, and internal capsule fibers from the superior temporal region.

This chapter discusses neurophysiological aspects of dynamics, including gaze, attention, and vocal signals during the perception of expressions. A link is established between the perception of facial dynamics and vocalization after examining behavioral and electrophysiological evidence. The similarity between eye-movement patterns of rhesus monkeys viewing dynamic vocalizing faces and human eye-movement patterns established a relationship between dynamic visual and vocalization behaviors for both monkeys and humans. Mimicry, which takes place at multiple levels of abstraction, plays a role in the perception of speech as it is triggered by the gaze and perception of expression. Dynamic social and nonsocial environmental cues have an impact on the importance of an emotional signal and the neural activity initiated by it.

The chapter is an extension of Hampton's approach of asking a monkey to respond metacognitively. It focuses on confidence judgments, which in humans are typically made verbally. It describes an experiment on rhesus macaque monkeys. These monkeys were given the opportunity to express their confidence by placing bets on the accuracy of their tasks in a cognitive task. The subjects were required to respond on all trials, easy and hard. After each trial, subjects were required to select a high- or a low-confidence icon. Having shown that the subjects chose the high- and low-confidence icons appropriately, this chapter argues that the metacognitive ability of monkeys is similar to that observed in human subjects in experiments that use the confidence judgment paradigm. Judgment of learning asks how certain they are that they will be able to remember a recently learned item in the future.