Biomedical subjects

R A Andersen

Publications and source records attributed to R A Andersen.

At least 91 records · Page 5Linked to original sources

PubMed1994

Transparent motion perception as detection of unbalanced motion signals. III. Modeling.

In the preceding two companion articles we studied the conditions under which transparent motion perception occurs through psychophysical experiments, and investigated the underlining neural mechanisms through physiological recordings. The main finding of our perceptual experiments was that whenever a display has finely balanced motion signals in all local areas, it is perceptually nontransparent, and that transparent displays always contain motion signals in different directions that are either spatially unbalanced, or unbalanced in their disparity or spatial frequency contents. In the physiological experiments, we found two stages in the processing of transparent stimuli. The first stage is located primarily in area V1. At this stage motion measurements are made and V1 cells respond well to both the balanced, nontransparent stimuli and the unbalanced, perceptually transparent stimuli. The second stage is located primarily in area MT. MT cells show strong suppression between opposite directions of motion. The suppression for the unbalanced, transparent stimuli is significantly less than that for the balanced, nontransparent stimuli. Therefore, the activity in the second, MT stage correlates better with the perception of motion transparency than the first, V1 stage, which does not distinguish reliably between transparent and nontransparent motion. The above experiments suggest a two-stage model of motion perception with a motion measurement stage in V1 and an opponent-direction suppression stage in area MT. In this article we explicitly test this model through analysis and computer simulations, and compare the response of the model to the perceptual and physiological results using the same balanced and unbalanced stimuli we used in the experiments. In the first stage of the computational model, motion energies in different spatial frequency and disparity ranges are extracted from each local region. Similar to V1, this stage does not distinguish between the balanced and unbalanced stimuli. In the subsequent stage motion energies of opposite directions but with same spatial frequency and disparity contents suppress each other using subtractive or divisive inhibition. This stage responds significantly better to the transparent stimuli than to the nontransparent ones, in agreement with MT activity.

Animals↗

PubMed1994

Tuning of MST neurons to spiral motions.

Cells in the dorsal division of the medial superior temporal area (MSTd) have large receptive fields and respond to expansion/contraction, rotation, and translation motions. These same motions are generated as we move through the environment, leading investigators to suggest that area MSTd analyzes the optical flow. One influential idea suggests that navigation is achieved by decomposing the optical flow into the separate and discrete channels mentioned above, that is, expansion/contraction, rotation, and translation. We directly tested whether MSTd neurons perform such a decomposition by examining whether there are cells that are preferentially tuned to intermediate spiral motions, which combine both expansion/contraction and rotation components. The finding that many cells in MSTd are preferentially selective for spiral motions indicates that this simple three-channel decomposition hypothesis for MSTd does not appear to be correct. Instead, there is a continuum of patterns to which MSTd cells are selective. In addition, we find that MSTd cells maintain their selectivity when stimuli are moved to different locations in their large receptive fields. This position invariance indicates that MSTd cells selective for expansion cannot give precise information about the retinal location of the focus of expansion. Thus, individual MSTd neurons cannot code, in a precise fashion, the direction of heading by using the location of the focus of expansion. The only way this navigational information could be accurately derived from MSTd is through the use of a coarse, population encoding. Positional invariance and selectivity for a wide array of stimuli suggest that MSTd neurons encode patterns of motion per se, regardless of whether these motions are generated by moving objects or by motion induced by observer locomotion.

Animals↗

PubMed1993

Coordinate transformations in the representation of spatial information.

Coordinate transformations are an essential aspect of behavior. They are required because sensory information is coded in the coordinates of the sensory epithelia (e.g. retina, skin) and must be transformed to the coordinates of muscles for movement. In this review we will concentrate on recent studies of visual-motor transformations. The studies show that representations of space are distributed, being specified in the activity of many cells rather than in the activity of individual cells. Furthermore, these distributed representations appear to be derived by a specific operation, which systematically combines visual signals with eye and head position signals.

Animals↗

PubMed1992

The response of neurons in areas V1 and MT of the alert rhesus monkey to moving random dot patterns.

We studied the response of single units to moving random dot patterns in areas V1 and MT of the alert macaque monkey. Most cells could be driven by such patterns; however, many cells in V1 did not give a consistent response but fired at a particular point during stimulus presentation. Thus different dot patterns can produce a markedly different response at any particular time, though the time averaged response is similar. A comparison of the directionality of cells in both V1 and MT using random dot patterns shows the cells of MT to be far more directional. In addition our estimates of the percentage of directional cells in both areas are consistent with previous reports using other stimuli. However, we failed to find a bimodality of directionality in V1 which has been reported in some other studies. The variance associated with response was determined for individual cells. In both areas the variance was found to be approximately equal to the mean response, indicating little difference between extrastriate and striate cortex. These estimates are in broad agreement (though the variance appears a little lower) with those of V1 cells of the anesthetized cat. The response of MT cells was simulated on a computer from the estimates derived from the single unit recordings. While the direction tuning of MT cells is quite wide (mean half-width at half-height approximately 50 degrees) it is shown that the cells can reliably discriminate much smaller changes in direction, and the performance of the cells with the smallest discriminanda were comparable to thresholds measured with human subjects using the same stimuli (approximately 1.1 degrees). Minimum discriminanda for individual cells occurred not at the preferred direction, that is, the peak of their tuning curves, but rather on the steep flanks of their tuning curves. This result suggests that the cells which may mediate the discrimination of motion direction may not be the cells most sensitive to that direction.

Animals↗

PubMed1992

Evidence for the lateral intraparietal area as the parietal eye field.

It has long been appreciated that the posterior parietal cortex plays a role in the processing of saccadic eye movements. Only recently has it been discovered that a small cortical area, the lateral intraparietal area, within this much larger area appears to be specialized for saccadic eye movements. Unlike other cortical areas in the posterior parietal cortex, the lateral intraparietal area has strong anatomical connections to other saccade centers, and its cells have saccade-related responses that begin before the saccades. The lateral intraparietal area appears to be neither a strictly visual nor strictly motor structure; rather it performs visuomotor integration functions including determining the spatial location of saccade targets and forming plans to make eye movements.

Animals↗

PubMed1992

Developmental change in c(6)-aldehyde formation by soybean leaves.

Damage to plant leaves by wounding or freezing induces the production of large amounts of C(6)-compounds. However, the control of formation of these compounds in leaves is not yet clear. In the current study, C(6)-aldehyde formation by freeze-injured soybean leaves of different ages (based on the leaf positions on the plant) at stage R1 of plant development was investigated. The results demonstrate that C(6)-aldehyde formation by the soybean (Glycine max L.) leaves changes as leaves develop. Younger leaves produce high levels of C(6)-aldehydes, mainly composed of hexanal. Subsequently, as the leaves develop, the level of C(6)-aldehyde formation decreases markedly, followed by an increase with a large shift from hexanal to hexenals. Lipoxygenase and lipolytic acyl hydrolase activity was reduced, and, in contrast, hydroperoxide lyase activity increased. There was little difference in lipoxygenase substrate specificity for linoleic acid and linolenic acid, but hydroperoxide lyase preferentially utilized 13-hydroperoxy-9,11,15-octadecatrienoic acid. In the in vivo lipoxygenase substrate pool, the linoleic acid level declined and the relative level of linolenic acid increased. The change in ratios of linolenic acid to linoleic acid showed a similar trend during soybean leaf development to that of hexenals to hexanal.

Journal Article↗

PubMed1991

A more biologically plausible learning rule for neural networks.

Many recent studies have used artificial neural network algorithms to model how the brain might process information. However, back-propagation learning, the method that is generally used to train these networks, is distinctly "unbiological." We describe here a more biologically plausible learning rule, using reinforcement learning, which we have applied to the problem of how area 7a in the posterior parietal cortex of monkeys might represent visual space in head-centered coordinates. The network behaves similarly to networks trained by using back-propagation and to neurons recorded in area 7a. These results show that a neural network does not require back propagation to acquire biologically interesting properties.

Animals↗

PubMed1991

Sensorimotor transformation during eye movements to remembered visual targets.

For eye movements made to visual targets, the brain must transform the retinotopic coordinate frame of the visual system to that of the oculomotor plant. Ideally, responses should exactly match target demands. However, during eye movements to remembered targets, responses are spatially distorted. The transformation does not retain accurate retinotopic registration, having both constant and variable components of error. Generally, the constant pattern of distortion appears as a hypermetria for upward saccades and a hypometria for downward movements. Most of the error accumulates during the first 800 msec of memory-contingent delay. The results are interpreted with respect to theories of how spatial information may be coded and transformed.

Animals↗

PubMed1991

Human perception of structure from motion.

Novel dynamic random-do displays representing a rotating cylinder or a noise-field were used to investigate the perception of structure from motion (SFM) in humans. The finite lifetimes of the points allowed the study of spatiotemporal characteristics with smoothly moving stimuli. In one set of experiments subjects had to detect the change from the unstructured motion to the appearance of the cylinder in a reaction time task. In another set of experiments subjects had to distinguish these two stimuli in a two-alternative forced-choice task. The two major findings were: (1) a relatively constant point lifetime threshold (50-85 msec) for perceiving structure from motion. This threshold is similar to the threshold for estimating velocity and suggests that velocity measurements are used to process SFM; (2) long reaction times for detecting structure (approximately 1 sec). The build-up of performance with time and with increasing numbers of points reflects a process of temporal and spatial integration. We propose that this integration is achieved through the generation of a surface representation of the object. Information from single features on the object appears to be used to interpolate a surface between these local measurements allowing the system to improve perception over extended periods of time even though each feature is present only briefly. Selective masking of the stimulus produced characteristic impairments which suggest that both velocity measurements and surface interpolation are global processes.

Form Perception↗

PubMed1991

Effect of the metal in the reaction between metallothionein and antimetallothionein antibody.

1. An antimetallothionein antibody, raised against Cd-carrying metallothionein, was applied in Western blotting of metallothionein. 2. Treatment of the electroblotted nitrocellulose sheets with metals belonging to the periodic system transition groups Ib and IIb, or with Pb, Ni or Cr, considerably enhanced binding of anti-metallothionein. A similar effect was found when the electroblotted sheets were treated with the strong alkylator N-ethylmaleimide. 3. It seems that the binding of metal to metallothionein modifies the configuration of the antibody binding sites by the formation of metal thiolate complexes. 4. Metal treatment of the nitrocellulose sheets after electroblotting, but before application of the primary antibody, offers a convenient method for use in Western blotting to significantly potentiate the reaction between metallothionein and the antimetallothionein antibody.

Alkylation↗

PubMed1991

Reductive metabolism and protein binding of chromium(VI) by P450 protein enzymes.

The cytochrome P450-dependent reduction of Cr(VI) using reconstituted phospholipid vesicles containing purified preparation of various forms of rabbit and rat liver microsomal cytochrome P450 has been investigated. The alcohol-induced form of the rat, P450IIE1, was the most efficient enzyme, 7.2 +/- 0.40 nmol Cr/nmol P450/min, whereas the corresponding rates for rat P450IA1, rat IIB1, rabbit IIB4, rabbit IA2 and rabbit IIE1 were 1.7 +/- 0.09, 2.5 +/- 0.08, 1.6 +/- 0.08, 2.5 +/- 0.15 and 1.6 +/- 0.08 nmol Cr/nmol P450/min respectively. NADPH-cytochrome P450 reductase had Cr(VI) reductase activity which was dependent on enzyme concentration. Below 0.15 nmol P450 reductase/ml the sp. act. was low and constant, while at a higher concentration the activity was markedly dependent upon the amount of enzyme present. In a quantitative binding assay it was shown that binding of [51Cr]Cr(VI) to the catalytic enzymes was proportional to the enzyme concentration up to 0.8 nmol P450/ml, which caused binding of 70% of the total radioactivity. Analysis by SDS-PAGE and autoradiography exhibited binding to the individual catalytic proteins of [51Cr]Cr. EDTA treatment removed the radioactivity from the bands matching P450 and P450 reductase, indicating that Cr(III) is bound to the proteins. The reducing activity of both P450 and P450 reductase was potently inhibited by oxygen. The inhibitory effect of oxygen is not due to reoxidation of the reduced Cr and redox cycling. Rat P450IA1 ethoxycoumarin O deethylase activity was inhibited after preincubation with chromate (CrO4(2-). The P450 reductase inhibitor 2'-AMP stimulated the anaerobic P450 reductase dependent Cr(VI) reductase rate approximately 2-fold. Both CO and CCl4 inhibited the different P450 enzymes to various extents. With rabbit P450IIE1 CCl4 stimulated the Cr(VI) reduction approximately 4-fold, whereas the activity of the other enzymes was inhibited when the reconstituted system was incubated with CrO4(2-) and CCl4 prior to NADPH addition. Neither CO nor CCl4 affected the Cr(VI) reducing activity of the P450 reductase. The difference in CrO4(2-) reducing activity of the P450 enzymes and binding to the enzymes may be important for in vivo endoplasmic catalytic metabolism of CrO4(2-).

7-Alkoxycoumarin O-Dealkylase↗

PubMed1991

Mitogenicity and metallothionein induction: two separate effects of zinc ions on human mononuclear blood cells.

The mitogenic effect of elevated concentrations of zinc ions on human lymphocytes was found to be inhibited by the glucocorticoid hormone dexamethasone. The effect decreased progressively from complete block to partial inhibition when the culture period before the addition of dexamethasone was prolonged. In contrast, dexamethasone did not inhibit an induced formation of metallothionein in mononuclear cells. Furthermore, dexamethasone itself was found to induce small amounts of metallothionein. Apparently, the mitogenic effect and the induction of metallothionein by zinc ions in mononuclear cells occur by mutually independent mechanisms.

Cells, Cultured↗

PubMed1991

Effect of in vivo chromate, acetone and combined treatment on rat liver in vitro microsomal chromium(VI) reductive activity and on cytochrome P450 expression.

Cytochrome P450 (P450IIE1) in rat has previously been shown to exhibit high chromate [Cr(VI)] reductase activity (Mikalsen et al. 1991). The present study reports on the effect of chromate treatment in vivo in rats and on the modulating effect of acetone + fasting on chromium(VI) toxicity. No effect of intraperitoneal injection with 5 mg chromate/kg was observed, whereas 15 mg chromate/kg decreased the liver microsomal Cr(VI) reductase activity by about 30% in in vitro microsomal incubations. In addition, the P450 and cytochrome b5 contents were decreased by about 30% and 25% respectively. Acetone + fasting caused increases of total microsomal P450 and cytochrome b5 contents, associated with similar increases in apoproteins P450IIE1 and P450IIB1 + 2, and their corresponding mRNA, and apoprotein NADPH-P450 reductase, as well as NADPH-P450 reductase and microsomal Cr(VI) reductive activities. Related to acetone + fasting alone, when given in combination with chromate (15 mg/kg) the Cr(VI) reductive activity was decreased by about 30%, associated with decreases in the P450 and cytochrome b5 contents, 65% and 35% respectively. This further reduced the apoprotein levels of P450IIB1 + 2, P450IIE1, and NADPH-P450 reductase to 90%, 60%, and 40%, respectively, and the mRNA levels of P450IIB2 and P450IIE1. No effect was observed on NADPH-P450 reductase activity. This dose also caused some macroscopic alterations in the liver. In contrast, the P450IIE1 apoprotein level in the lung was apparently stabilized or even increased by chromate in rats treated with acetone + fasting.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetone↗

PubMed1991

Saccade-related activity in the lateral intraparietal area. I. Temporal properties; comparison with area 7a.

1. The cortex of the inferior parietal lobule (IPL) contains neurons whose activity is related to saccadic eye movements. The exact role of the IPL in relation to saccades remains, however, unclear. In this and the companion paper, we approach this problem by quantifying many of the spatial and temporal parameters of the saccade-related (S) activity. These parameters have hitherto been largely unstudied. 2. The activity of single neurons was recorded from Macaca mulatta monkeys while they were performing a delayed-saccade task. The analysis presented here is based on 161 neurons recorded from the lateral intraparietal area (LIP), a recently defined subdivision of the IPL; and 54 neurons recorded from the neighboring part of the IPL, area 7a. Overall, 409 IPL neurons were isolated in this study. 3. The typical activity of IPL neurons during the delayed-saccade task has three basic phases: light sensitive (LS), memory (M), and S. These basic phases are common to neurons of both areas LIP and 7a. In each phase (LS, M, and S), individual neurons may or may not be active. Most LIP neurons, however, are active in more than one phase. 4. To compare the activity levels of different neurons, the actual firing rate was weighted by each neuron's background level, yielding an "activity index" for each neuron, in each phase of the task. We calculated the activity index for the LS and M phases and for three phases related to the saccade: a presaccadic (Pre-S), a saccade-coincident (S-Co), and a postsaccadic (Post-S) phase. For area LIP neurons the median values of the activity index were high for the LS, M, Pre-S, and S-Co activities, and slightly lower in the Post-S period. In area 7a the median values were low for the LS phase and, in particular, for the M and Pre-S phases, somewhat higher coincident with the saccade, and high post-saccadically. 5. In area LIP, in each phase, 49-63% of the neurons had excitatory activity, and 10-17% had inhibitory responses. 6. In contrast, in area 7a excitatory responses were most frequent in the Post-S phase (56%). Excitation was particularly infrequent during M (28%) and Pre-S (22%). The incidence of inhibitory responses varied too (4-18%). The time course of inhibition was roughly opposite that of excitation; the highest frequency of inhibitory responses occurred during the saccade.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Saccade-related activity in the lateral intraparietal area. II. Spatial properties.

1. Single-neuron activity was recorded from the inferior parietal lobule (IPL) of Macaca mulatta monkeys while they were performing delayed saccades and related tasks. Temporal characteristics of this activity were presented in the companion paper. Here we focus on the spatial characteristics of the activity. The analysis was based on recordings from 145 neurons. All these neurons were from the lateral intraparietal area (LIP), a recently defined subdivision of the IPL. 2. Delayed saccades were made in eight directions. Direction-tuning curves were calculated for each neuron, during each of the following activity phases that were described in the companion paper: light sensitive (LS), delay-period memory (M), and saccade related (S); the latter further partitioned into presaccadic (Pre-S), saccade coincident (S-Co), and postsaccadic (Post-S). 3. Width and preferred direction were calculated for each direction-tuning curve. We studied the distributions of widths and preferred directions in LIP's neuronal population. In each case we included only neurons that showed clear excitatory activity in the phases in question. 4. Width was defined as the angle over which the response was higher than 50% of its maximal net value. Width distributions were similar for all phases studied. Widths varied widely from neuron to neuron, from very narrow (less than 45 degrees) to very wide (close to 360 degrees). Median widths were approximately 90 degrees in all phases. 5. Preferred-direction distributions were also similar for various phases. All directions were represented in each distribution, but contralateral directions were more frequent (e.g., 69% for S-Co). 6. For each neuron the alignment of the preferred directions of its various phases was determined. Distributions of alignments were calculated (again, phases that were not clearly excitatory were disregarded). On the level of the neuronal population LS, M, and Pre-S were well aligned with each other. S-Co was also aligned with these phases, but less precisely. 7. A set of "narrowly tuned" neurons was selected by imposing a constraint of narrow (width, less than 90 degrees) LS and S-Co direction tuning. In this set of neurons, the LS and S-Co preferred directions were very well aligned (median, 12 degrees). The fraction of narrowly tuned neurons in the population was 40% (25/63). Thus, in a large subpopulation of area LIP, a fairly precise alignment exists between sensory and motor fields. 8. An additional set of 82 area LIP neurons were recorded while the monkey performed delayed saccades to 32 targets located on small, medium, and large imaginary circles.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

The response of area MT and V1 neurons to transparent motion.

An important use of motion information is to segment a complex visual scene into surfaces and objects. Transparent motions present a particularly difficult problem for segmentation because more than one velocity vector occurs at each local region in the image, and current machine vision systems fail in these circumstances. The fact that motion transparency is prevalent in natural scenes, and yet artificial systems display an inability to analyze it, suggests that the primate visual system has developed specialized methods for perceiving transparent motion. Also, the currently prevalent model of physiological mechanisms for motion-direction selectivity employs inhibitory interactions between neurons; such interactions would silence neurons under transparent conditions and render the visual system blind to transparent motion. To examine how the primate visual system solves this transparency problem, we recorded the activity of direction-selective cells in the first (area V1) and in a later (area MT) stage in the cortical motion-processing pathway in behaving monkeys. The visual stimuli consisted of random dot patterns forming single moving surfaces, transparent surfaces, and motion discontinuities. We found that area V1 cells responded to their preferred direction of movement even under transparent conditions, whereas area MT cells were suppressed under the transparent condition. These data suggest a simple solution to the transparency problem at the level of area V1. More than one motion vector can be represented at a single retinal location by different subpopulations of neurons tuned to different directions of motion; these subpopulations may represent the early stage for segmenting different, transparent surfaces. The results also suggest that facilitatory mechanisms, which unlike inhibitory interactions are largely unaffected by transparent conditions, play an important role in direction selectivity in area V1. The inhibitory interactions for different motion directions for area MT neurons may contribute to a mechanism for smoothing or averaging the velocity field, computations thought to be necessary for reducing noise and interpolating moving surfaces from sparse information.

Animals↗

PubMed1990

Visual receptive field organization and cortico-cortical connections of the lateral intraparietal area (area LIP) in the macaque.

The visual receptive field physiology and anatomical connections of the lateral intraparietal area (area LIP), a visuomotor area in the lateral bank of the inferior parietal lobule, were investigated in the cynomolgus monkey (Macaca fascicularis). Afferent input and physiological properties of area 5 neurons in the medial bank of the intraparietal sulcus (i.e., area PEa) were also determined. Area LIP is composed of two myeloarchitectonic zones: a ventral zone (LIPv), which is densely myelinated, and a lightly myelinated dorsal zone (LIPd) adjacent to visual area 7a. Previous single-unit recording studies in our laboratory have characterized visuomotor properties of area LIP neurons, including many neurons with powerful saccade-related activity. In the first part of the present study, single-unit recordings were used to map visual receptive fields from neurons in the two myeloarchitectonic zones of LIP. Receptive field size and eccentricity were compared to those in adjacent area 7a. The second part of the study investigated the cortico-cortical connections of area LIP neurons using tritiated amino acid injections and fluorescent retrograde tracers placed directly into different rostrocaudal and dorsoventral parts of area LIP. The approach to area LIP was through somatosensory area 5, which eliminated the possibility of diffusion of tracers into area 7a. Unlike many area 7a receptive fields, which are large and bilateral, area LIP receptive fields were much smaller and exclusively confined to the contralateral visual field. In area LIP, an orderly progression in visual receptive fields was evident as the recording electrode moved tangentially to the cortical surface and through the depths of area LIP. The overall visual receptive field organization, however, yielded only a rough topography with some duplications in receptive field representation within a given rostrocaudal or dorsoventral part of LIP. The central visual field representation was generally located more dorsally and the peripheral visual field more ventrally within the sulcus. The lower visual field was represented more anteriorly and the upper visual field more posteriorly. In LIP, receptive field size increased with eccentricity but with much variability with in the sample. Area LIPv was found to have reciprocal cortico-cortical connections with many extrastriate visual areas, including the parieto-occipital visual area PO; areas V3, V3A, and V4: the middle temporal area (MT); the middle superior temporal area (MST); dorsal prelunate area (DP); and area TEO (the occipital division of the intratemporal cortex). Area LIPv is also connected to area TF in the lateral posterior parahippocampal gyrus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Corticocortical connections of anatomically and physiologically defined subdivisions within the inferior parietal lobule.

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)

Animals↗