The cortex of the inferior parietal lobule in primates is important for spatial perception and spatially oriented behavior. Recordings of single neurons in this area in behaving monkeys showed that the visual sensitivity of the retinotopic receptive fields changes systematically with the angle of gaze. The activity of many of the neurons can be largely described by the product of a gain factor that is a function of the eye position and the response profile of the visual receptive field. This operation produces an eye position-dependent tuning for locations in head-centered coordinate space.

The anatomical and functional organization of the inferior parietal lobule was investigated in macaque monkeys by using anterograde and retrograde anatomical tracing techniques and single cell recording techniques in awake, behaving monkeys. The connections of areas 7a and 7b, and of two previously unexplored areas, the lateral intraparietal area (LIP) and the dorsal prelunate area (DP), were examined in detail. Functional mapping experiments were performed in all four areas. Prior to this study the pathways for visual input to area 7a were unclear. In these experiments we found several direct projections from extrastriate visual areas, including the lateral intraparietal (LIP), dorsal prelunate (DP), parieto-occipital (PO), and medial superior temporal (MST) areas into area 7a. Using the observed laminar patterns of connections between areas 7a, LIP, and DP and other extrastriate cortical areas, we were able to construct a hypothetical flow of visual information processing from striate cortex to area 7a. A broader hierarchy was also produced, which relates the positions of areas 7a, 7b, LIP, and DP to various cortical fields in the parietal, temporal, and frontal lobes. By combining single cell recording techniques in trained monkeys with anatomical tracing techniques, we have parceled the inferior parietal lobule into several subdivisions on the basis of both anatomical and physiological grounds. A clear segregation of visual and somatosensory responses was found in the inferior parietal lobule with areas 7a, LIP, and DP being visual and visual-motor and area 7b being primarily somatosensory. A similar segregation was found anatomically with areas 7a, LIP, and DP being interconnected primarily with other visual cortical areas and area 7b being connected with several somatosensory areas. Area 7b was also found to connect to a few visual cortical areas, and these connections likely account for the small but consistent number of visually responsive cells that are found in this region. Areas LIP, DP, and 7a differed in receptive field and saccade-related properties. Area 7a visual receptive fields were very large and usually bilateral with a small but significant number of them having receptive field centers in the ipsilateral visual field. Area DP and LIP receptive fields were smaller and the receptive field peaks were almost always confined to the contralateral visual field. Areas 7a, DP, and LIP all contained cells with saccade-related responses; however, in area 7a there were fewer saccade cells than area LIP, and presaccadic responses were only observed in area LIP.(ABSTRACT TRUNCATED AT 400 WORDS)

Behavioral and clinical studies have long implicated the posterior parietal cortex of primates in spatial perception and spatially oriented behavior. However, recordings from single neurons in behaving monkeys by different laboratories have resulted in divergent views with some ascribing a largely motor and others a largely sensory role for this region. We have designed paradigms to separate the sensory and motor components of the neural activity and have found that the cells in this area respond to both sensory stimulation and motor behavior. Thus, it is likely that this area is not solely sensory or motor, but rather is involved in higher order aspects of sensory-motor integration.

Environmentally relevant stimuli were used to examine the selectivity of area 7a neurons to optic flow using moving, flickering dots. Monkeys performed a psychophysical task requiring them to detect changes in translation, rotational and radially structured optic flow fields consisting of collections of moving dots which are free of form cues. The neurons in area 7a were selectively responsive to all the different types of moving stimuli. Two types of tuning for motion selectivity were found. Some neurons were tuned to distinguish a particular direction of optic flow (e.g. radial expansion versus radial compression), while others were tuned to distinguish between different classes of optic flow (e.g. radial motion versus planar rotation). The latter tuning was unlike that reported for area MST by others and may represent a novel representation of optic flow. The response of these neurons to translating bars was compared to that of optic flow fields. There appeared to be no similarity in the tuning to the two types of motion. Furthermore, there does not appear to be an identity between the neurons that could be classified as opponent vector and those selective for radial optic flow. Area 7a is involved in the further analysis of optic flow beyond the cortical areas MT and MST and provides a novel representation of motion. These results are consistent with the neurons in area 7a utilizing motion for the construction of a spatial representation of extra-personal space.

Optical imaging of the functional architecture of cortex, based on intrinsic signals, is a useful tool for the study of the development, organization, and function of the living mammalian brain. This relatively noninvasive technique is based on small activity-dependent changes of the optical properties of cortex. Thus far, functional imaging has been performed only on anesthetized animals. Here we establish that this technique is also suitable for exploring the brain of awake behaving primates. We designed a chronic sealed chamber and mounted it on the skull of a cynomolgus monkey (Macaca fasciculatis) over the primary visual cortex to permit imaging through a transparent glass window. Restriction of head position alone was sufficient to eliminate movement noise in awake monkey imaging experiments. High-resolution imaging of the ocular dominance columns and the cytochrome oxidase blobs was achieved simply by taking pictures of the exposed cortex when the awake monkey was viewing video movies alternatively with each eye. Furthermore, the functional maps could be obtained without synchronization of the data acquisition to the animal's respiration and the electrocardiogram. The wavelength dependency and time course of the intrinsic signal were similar in anesthetized and awake monkeys, indicating that the signal sources were the same. We therefore conclude that optical imaging is well suited for exploring functional organization related to higher cognitive brain functions of the primate as well as providing a diagnostic tool for delineating functional cortical borders and assessing proper functions of human patients during neurosurgery.The awake monkey preparation has offered many advantages for the study of higher cognitive functions (1). First, there are many questions that cannot be investigated by using anesthetized animals, simply because the brain of the anesthetized animal cannot perform the same remarkable computational tasks that the awake brain performs, especially in cortical regions other than primary sensory areas (2-6). Second, by manipulating the animal's behavior, it has been possible to begin to answer questions about the neuronal basis of higher cognitive functions. For example, how does the response of the neurons depend on behavioral states of the animal such as attention and motivation (7-10)? Finally, long-term physiological studies are possible in awake primates, allowing the investigation of development (11) and plasticity of the brain (12, 13).Single unit recordings have been used for most of the recent explorations in the awake monkey preparation (12)(13)(14)(15)(16). This powerful technique is limited, however, to the measurement of the activity of very few neurons at a time. Local field potential measurement of brain activity has been made (17-19); however, its resolution is inadequate for high-resolution functional mapping of cortex. Furthermore, the interpretation of the results may be difficult due to the nonisotropic electrical properties of cortical tissue.Two optical method...