Primate Cerebral Cortex Research Articles

The Main Afferent Fiber Systems of the Cerebral Cortex in Primates. An Investigation of the Central Portions of the Somato-Sensory, Auditory, and Visual Paths of the Cerebral Cortex, with Consideration of Their Normal and Pathological Function, Based on Experiments with Monkeys.

This fine monograph is a preliminary, and a necessary one, to a study of the comparatively little known association connections of various cortical areas as determined by cyto-architectural and myelo-architectural investigations. To obtain results applicable to human physiology and pathology, the experiments were carried out on monkeys (Macacus rhesus, except in one case in which a Java monkey was used). The experiments consisted of interruptions of the afferent projection fiber systems at or near their origin from the diencephalon, thereby causing their partial or complete secondary degeneration, avoiding at the same time as far as possible other fiber systems. The secondarily degenerated fibers were traced to their respective terminations in the cortex, and the internal arrangements of the three afferent paths investigated (somatosensory, auditory and visual), the cortical areas in which they terminated and the finer relation of their fibers to the cortex were studied. The staining method used was

THE PREVENTION OF DIFFICULT LABOUR

<h3>Abstract</h3> Neurons in the Middle Temporal area (MT) of the primate cerebral cortex respond to moving visual stimuli. The sensitivity of MT neurons to motion signals can be characterized by using random-dot stimuli, in which the strength of the motion signal is manipulated by adding different levels of noise (elements that move in random directions). In macaques, this has allowed the calculation of “neurometric” thresholds. We characterized the responses of MT neurons in sufentanil/nitrous oxide anesthetized marmoset monkeys, a species which has attracted considerable recent interest as an animal model for vision research. We found that MT neurons show a wide range of neurometric thresholds, and that the responses of the most sensitive neurons could account for the behavioral performance of macaques and humans. We also investigated factors that contributed to the wide range of observed thresholds. The difference in firing rate between responses to motion in the preferred and null directions was the most effective predictor of neurometric threshold, whereas the direction tuning bandwidth had no correlation with the threshold. We also showed that it is possible to obtain reliable estimates of neurometric thresholds using stimuli that were not highly optimized for each neuron, as is often necessary when recording from large populations of neurons with different receptive field concurrently, as was the case in this study. These results demonstrate that marmoset MT shows an essential physiological similarity to macaque MT, and suggest that its neurons are capable of representing motion signals that allow for comparable motion-in-noise judgments. <h3>New and Noteworthy</h3> We report the activity of neurons in marmoset MT in response to random-dot motion stimuli of varying coherence. The information carried by individual MT neurons was comparable to that of the macaque, and that the maximum firing rates were a strong predictor of sensitivity. Our study provides key information regarding the neural basis of motion perception in the marmoset, a small primate species that is becoming increasingly popular as an experimental model.