Temporal Cortical Visual Areas Research Articles

Extensive cortical functional connectivity of the human hippocampal memory system

The cortical connections of the human hippocampal memory system are fundamental to understanding its operation in health and disease, especially in the context of the great development of the human cortex. The functional connectivity of the human hippocampal system was analyzed in 172 participants imaged at 7T in the Human Connectome Project. The human hippocampus has high functional connectivity not only with the entorhinal cortex, but also with areas that are more distant in the ventral ‘what’ stream including the perirhinal cortex and temporal cortical visual areas. Parahippocampal gyrus TF in humans has connectivity with this ventral ‘what’ subsystem. Correspondingly for the dorsal stream, the hippocampus has high functional connectivity not only with the presubiculum, but also with areas more distant, the medial parahippocampal cortex TH which includes the parahippocampal place or scene area, the posterior cingulate including retrosplenial cortex, and the parietal cortex. Further, there is considerable cross connectivity between the ventral and dorsal streams with the hippocampus. The findings are supported by anatomical connections, which together provide an unprecedented and quantitative overview of the extensive cortical connectivity of the human hippocampal system that goes beyond hierarchically organised and segregated pathways connecting the hippocampus and neocortex, and leads to new concepts on the operation of the hippocampal memory system in humans.

The evolution and functions of nuclei of the visual pulvinar in primates.

In this review, we outline the history of our current understanding of the organization of the pulvinar complex of mammals. We include more recent evidence from our own studies of both New and Old World monkeys, prosimian galagos, and close relatives of primates, including tree shrews and rodents. Based on cumulative evidence, we provide insights into the possible evolution of the visual pulvinar complex, as well as the possible co-evolution of the inferior pulvinar nuclei and temporal cortical visual areas within the MT complex.

Memory systems in the brain.

The operation of different brain systems involved in different types of memory is described. One is a system in the primate orbitofrontal cortex and amygdala involved in representing rewards and punishers, and in learning stimulus-reinforcer associations. This system is involved in emotion and motivation. A second system in the temporal cortical visual areas is involved in learning invariant representations of objects. A third system in the hippocampus is implicated in episodic memory and in spatial function. Fourth, brain systems in the frontal and temporal cortices involved in short term memory are described. The approach taken provides insight into the neuronal operations that take place in each of these brain systems, and has the aim of leading to quantitative biologically plausible neuronal network models of how each of these memory systems actually operates.

Consciousness in Neural Networks?

A combined neurophysiological and computational approach is reviewed that leads to a proposal for how neural networks in the temporal cortical visual areas of primates could function to produce invariant object representation and identification. A similar approach is then reviewed which leads to a theory of how the hippocampus could rapidly store memories, especially episodic memories including spatial context, and how later recall of the information to the neocortex could occur. Third, it is argued that the visual and memory mechanisms described could operate without consciousness, and that a different type of processing is related to consciousness. It is suggested that the type of processing related to consciousness involves higher-order thoughts ("thoughts about thoughts"), and evolved to allow plans, formulated in a language, with many steps, to be corrected. It is suggested that it would feel like something to be a system that can think linguistically (using syntax) about its own thoughts, and that the subjective or phenomenal aspects of consciousness arise in this way. It is further suggested that "raw sensory feels" arise in evolution because once some types of processing feel like something by virtue of a system capable of higher-order thoughts, it is then parsimonious to postulate that sensory and related processing, which has to be taken into account in that processing system, should feel like something. It is suggested that it is this type of processing, which must be implemented in neural networks, which is related to consciousness.

INVARIANT FACE AND OBJECT RECOGNITION IN THE VISUAL SYSTEM

Neurophysiological evidence is described, showing that some neurons in the macaque temporal cortical visual areas have responses that are invariant with respect to the position, size and view of faces and objects, and that these neurons show rapid processing and rapid learning. A theory is then described of how such invariant representations may be produced in a hierarchically organized set of visual cortical areas with convergent connectivity. The theory proposes that neurons in these visual areas use a modified Hebb synaptic modification rule with a short-term memory trace to capture whatever can be captured at each stage that is invariant about objects as the object changes in retinal position, size, rotation and view. Simulations are then described which explore the operation of the architecture. The simulations show that such a processing system can build invariant representations of objects. © 1977 Elsevier Science Ltd. All Rights Reserved.

Response properties of neurons in temporal cortical visual areas of infant monkeys.

1. Inferior temporal cortex (IT) is a "high-order" region of primate temporal visual cortex implicated in visual pattern perception and recognition. To gain some insight into the development of this area, we compared the properties of single neurons in IT in infant monkeys ranging from 5 wk to 7 mo of age with those of neurons in IT in adult animals. Both anesthetized and awake behaving paradigms were used. 2. In immobilized infant monkeys under nitrous oxide anesthesia, the incidence of visually responsive cells was markedly less than in adult monkeys studied under similar conditions. In infants 4-7 mo of age, only half of IT neurons studied were visually responsive, compared with > 80% in adult monkeys. In monkeys < 4 mo old, even fewer (< 10%) could be visually driven. "Habituation" of IT cells to repeated stimulus presentation appeared more pronounced in infant monkeys under nitrous oxide anesthesia than in adult animals. 3. IT cells in the anesthetized infant monkeys that did respond showed receptive field properties similar to those of responsive adult IT neurons studied under similar conditions. Two thirds of the receptive fields plotted in the anesthetized 4 to 7-mo-old group were bilateral, and median field size did not differ between the infants and comparable adult groups, being approximately 20 degrees on a side in each case. 4. In contrast to the results obtained under anesthesia, most IT cells in alert infant monkeys 5 wk-7 mo of age (80%) were responsive to visual stimuli, and this incidence of visually responsive IT neurons did not differ from that obtained in awake adult macaques. However, response magnitude, measured as spikes per second above baseline rate, was significantly lower in the infant alert sample than in the adult control (5.2 vs. 12.6 spikes/s, mean +/- SE, deviation from spontaneous rate, respectively). 5. In addition to having lower magnitudes of visual response, IT cells in the awake infants also tended to have longer and more variable latencies. The overall mean for the infant cells was 196 ms, compared with an overall mean of 140 ms for IT neurons in the alert control adult. 6. Although the magnitude of response of neurons in alert infant IT cortex was lower overall, the incidence and features of stimulus selectivity shown by alert infant IT neurons were strikingly similar to those of IT cells of both anesthetized and unanesthetized adult monkeys.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurophysiological mechanisms underlying face processing within and beyond the temporal cortical visual areas.

The ways in which information about faces is represented and stored in the temporal lobe visual areas of primates, as shown by recordings from single neurons in macaques, are considered. Some neurons that respond primarily to faces are found in the cortex in the anterior part of the superior temporal sulcus (in which neurons are especially likely to be tuned to facial expression and to face movement involved in gesture), and in the TE areas more ventrally forming the inferior temporal gyrus (in which neurons are more likely to have responses related to the identity of faces). Quantitative studies of the responses of the neurons that respond differently to the faces of different individuals show that information about the identity of the individual is represented by the responses of a population of neurons, that is, ensemble encoding rather than 'grandmother cell' encoding is used. It is argued that this type of tuning is a delicate compromise between very fine tuning, which has the advantage of low interference in neuronal network operations but the disadvantage of losing the useful properties (such as generalization, completion and graceful degradation) of storage in neuronal networks, and broad tuning, which has the advantage of allowing these properties of neuronal networks to be realized but the disadvantage of leading to interference between the different memories stored in an associative network. There is evidence that the responses of some of these neurons are altered by experience so that new stimuli become incorporated in the network. It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation. Thus the representation is in a form which is particularly useful for storage and as an output from the visual system. It is also shown that one of the representations that is built is object based, which is suitable for recognition and as an input to associative memory, and that another is viewer centred, which is appropriate for conveying information about gesture. Ways are considered in which such cortical representations might be built by competitive self-organization aided by back projections in the multi-stage cortical processing hierarchy which has convergence from stage to stage.

Neural organization of higher visual functions

This paper reviews recent progress made with both anatomical and neurophysiological techniques in understanding the neural organization of higher visual functions in V4, the temporal cortical visual areas, and brain regions connected to these, such as the striatum and amygdala.

Responses of neurons in the inferior temporal cortex in short term and serial recognition memory tasks.

Gaffan and Weiskrantz (1980) and Mishkin (1982) have shown that lesions to the inferior temporal visual cortex can impair the performance of serial visual recognition memory tasks. In order to provide evidence on whether the inferior temporal visual cortex contains a mechanism which enables memory to span the intervening items in a serial recognition task, or whether the inferior temporal cortex is merely afferent to such recent memory mechanisms, we analysed the activity of single neurons in the inferior temporal visual cortex and the adjacent cortex in the superior temporal sulcus in both delayed match to sample and serial recognition memory tasks. In the serial recognition task, various numbers of stimuli intervened between the first and second presentations of a stimulus. A considerable proportion (64/264 or 26%) of visually responsive inferotemporal neurons showed a different response to the "novel" and "familiar" presentations of a stimulus in the serial recognition memory task, and often a corresponding difference in response between the sample and match presentations of a stimulus in the delayed match to sample task. For the majority of neurons this difference was not sustained across even one intervening stimulus in the serial recognition task, and no neurons bridged more than 2 intervening stimuli. These results show that neurons in the inferior temporal cortex have responses which would be useful for a short term visual memory for stimuli, but would not be useful in recency memory tasks in which more than one stimulus intervenes between the first and second presentations of a stimulus. In this investigation, neurons were recorded both in the cortex on the inferior temporal gyrus (commonly called inferior temporal visual cortex, and consisting of areas TE3, TE2 and TE1 of Seltzer and Pandya 1978), and in the cortex in the adjacent anterior part of the superior temporal sulcus, in which a number of different temporal cortical visual areas have now been described.