Superior Temporal Polysensory Area Research Articles

Encoding of vestibular and optic flow cues to self-motion in the posterior superior temporal polysensory area.

Neurons in the posterior superior temporal polysensory area (STPp) showed significant directional selectivity in response to vestibular, optic flow and combined visual-vestibular stimuli. By comparison to the dorsal medial superior temporal area, the visual latency was slower in STPp but the vestibular latency was faster. Heading preferences under combined stimulation in STPp were usually dominated by visual signals. Cross-modal enhancement was observed in STPp when both vestibular and visual cues were presented together at their heading preferences. Human neuroimaging data implicated that the superior temporal polysensory area (STP) might be involved in vestibular-visual interaction during heading computations, but the heading selectivity has not been examined in the macaque. Here, we investigated the convergence of optic flow and vestibular signals in macaque STP by using a virtual-reality system and found that 6.3% of STP neurons showed multisensory responses, with visual and vestibular direction preferences either congruent or opposite in roughly equal proportion. The percentage of vestibular-tuned cells (18.3%) was much smaller than that of visual-tuned cells (30.4%) in STP. The vestibular tuning strength was usually weaker than the visual condition. The visual latency was significantly slower in STPp than in the dorsal medial superior temporal area (MSTd), but the vestibular latency was significantly faster than in MSTd. During the bimodal condition, STP cells' response was dominated by visual signals, with the visual heading preference not affected by the vestibular signals but the response amplitudes modulated by vestibular signals in a subadditive way.

Involvement of the superior temporal cortex in action execution and action observation.

The role of the superior temporal sulcus (STs) in action execution and action observation remains unsettled. In an attempt to shed more light on the matter, we used the quantitative method of (14)C-deoxyglucose to reveal changes in activity, in the cortex of STs and adjacent inferior and superior temporal convexities of monkeys, elicited by reaching-to-grasp in the light or in the dark and by observation of the same action executed by an external agent. We found that observation of reaching-to-grasp activated the components of the superior temporal polysensory area [STP; including temporo-parieto-occipital association area (TPO), PGa, and IPa], the motion complex [including medial superior temporal area (MST), fundus of superior temporal area (FST), and dorsal and ventral parts of the middle temporal area (MTd and MTv, respectively)], and area TS2. A significant part of most of these activations was associated with observation of the goal-directed action, and a smaller part with the perception of arm-motion. Execution of reaching-to-grasp in the light-activated areas TS2, STP partially and marginally, and MT compared with the fixation but not to the arm-motion control. Consequently, MT-activation is associated with the arm-motion and not with the purposeful action. Finally, reaching-to-grasp in complete darkness activated all components of the motion complex. Conclusively, lack of visibility of our own actions involves the motion complex, whereas observation of others' actions engages area STP and the motion complex. Our previous and present findings together suggest that sensory effects are interweaved with motor commands in integrated action codes, and observation of an action or its execution in complete darkness triggers the retrieval of the visual representation of the action.

View-Based Encoding of Actions in Mirror Neurons of Area F5 in Macaque Premotor Cortex

Converging experimental evidence indicates that mirror neurons in the monkey premotor area F5 encode the goals of observed motor acts [1-3]. However, it is unknown whether they also contribute to encoding the perspective from which the motor acts of others are seen. In order to address this issue, we recorded the visual responses of mirror neurons of monkey area F5 by using a novel experimental paradigm based on the presentation of movies showing grasping motor acts from different visual perspectives. We found that the majority of the tested mirror neurons(74%) exhibited view-dependent activity with responses tuned to specific points of view. A minority of the tested mirror neurons (26%) exhibited view-independent responses. We conclude that view-independent mirror neurons encode action goals irrespective of the details of the observed motor acts, whereas the view-dependent ones might either form an intermediate step in the formation of view independence or contribute to a modulation of view-dependent representations in higher-level visual areas, potentially linking the goals of observed motor acts with their pictorial aspects.

Long-range coupling of prefrontal cortex and visual (MT) or polysensory (STP) cortical areas in motion perception

Event Abstract Back to Event Long-range coupling of prefrontal cortex and visual (MT) or polysensory (STP) cortical areas in motion perception Lucia M. Vaina1, 2*, Finnegan Calabro1, Fa-Hsuan Lin2 and Matti Hamalainen3 1 Boston University, United States 2 Harvard University, United States 3 Massachusetts General Hospital, United States To investigate how, where and when moving auditory cues interact with the perception of object-motion during self-motion, we conducted psychophysical, and MEG experiments in which the subjects viewed nine textured objects during simulated forward self-motion. On each trial, one object was randomly assigned its own looming motion within the scene. Subjects reported which of four labeled objects had independent motion within the scene in two conditions: (1) visual information only and (2) with additional auditory cue. In psychophysics, observers performed slightly better in the presence of an auditory cue moving in the same direction with the object target (p=0.003, t=4.18, df=8, min 1.2%, and max 8.1). When the auditory cue was static, uninformative, it had not impact on performance. In cortically-constrained MEG source estimates, comparison of the two conditions showed: (i) MT (middle temporal area) activity similar across conditions; (ii) additional activity in the auditory cue condition ventral to MT late after the stimulus presentation; (iii) with the auditory cue, early activity at the right auditory cortex (AC) together with STP (superior temporal polysensory area), (iv) different time courses of these two activities with STP signals later in the epoch together with frontal activity in the right hemisphere, (v) stronger activity in PPC (posterior parietal cortex) in the visual-only condition than in the auditory-cue condition. In addition, Dynamic Granger Causality analysis among cortical regions showed for the auditory cues condition a strong connection of the AC with STP but not with MT suggesting binding of visual and auditory information at STP. Also, while in the visual-only condition PFC is connected with MT, in the auditory-cue condition PFC (prefrontal cortex) is connected to STP. These results indicate that PFC allocates attention to the “object” as a whole, in STP to a moving visual-auditory object, and in MT to a moving visual object. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Sensory Processing and Functional Connectivity Citation: Vaina LM, Calabro F, Lin F and Hamalainen M (2010). Long-range coupling of prefrontal cortex and visual (MT) or polysensory (STP) cortical areas in motion perception. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00212 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Mar 2010; Published Online: 30 Mar 2010. * Correspondence: Lucia M Vaina, Boston University, Boston, United States, vaina@bu.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen Google Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen Google Scholar Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen PubMed Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Multisensory connections of monkey auditory cerebral cortex

Functional studies have demonstrated multisensory responses in auditory cortex, even in the primary and early auditory association areas. The features of somatosensory and visual responses in auditory cortex suggest that they are involved in multiple processes including spatial, temporal and object-related perception. Tract tracing studies in monkeys have demonstrated several potential sources of somatosensory and visual inputs to auditory cortex. These include potential somatosensory inputs from the retroinsular (RI) and granular insula (Ig) cortical areas, and from the thalamic posterior (PO) nucleus. Potential sources of visual responses include peripheral field representations of areas V2 and prostriata, as well as the superior temporal polysensory area (STP) in the superior temporal sulcus, and the magnocellular medial geniculate thalamic nucleus (MGm). Besides these sources, there are several other thalamic, limbic and cortical association structures that have multisensory responses and may contribute cross-modal inputs to auditory cortex. These connections demonstrated by tract tracing provide a list of potential inputs, but in most cases their significance has not been confirmed by functional experiments. It is possible that the somatosensory and visual modulation of auditory cortex are each mediated by multiple extrinsic sources.

Cortical Connections of the Macaque Caudal Ventrolateral Prefrontal Areas 45A and 45B

We have found that the 2 architectonic subdivisions of the prefrontal area 45, 45A and 45B, display connectivity patterns that clearly distinguish them from one another and from their neighboring architectonic areas. Area 45A is primarily connected to the frontal areas 45B, 12l, caudal 12r, 12o, 10, rostrodorsal 46, 9/8B, 44, 8/FEF (frontal eye field), and the SEF (supplementary eye field), temporal area IPa, and unique among all the studied areas, to the superior temporal polysensory (STP) area and auditory parabelt areas. Area 45B displayed much stronger frontal connections with the oculomotor areas 8/FEF, 8r, and the SEF than those of area 45A, primary connections with areas 12l, caudal 12r, 12o, and 8B, and unlike area 45A, with areas ventrorostral 46, rostral 12r, 12m, and 13m. Temporal connections were all virtually confined to areas IPa, intermediate TEa/m, and TE. Additional labeling was found in lateral intraparietal area. Our data suggest that 45A and 45B are 2 distinct areas, possibly playing a differential role in nonspatial information processing: area 45A corresponds to the prefrontal sector for which a role in communication behavior and homology with the human area 45 was proposed, whereas area 45B is a distinct prearcuate area, possibly affiliated to the oculomotor frontal system.

Electrophysiological correlates of affective blindsight

An EEG investigation was carried out in a patient with complete cortical blindness who presented affective blindsight, i.e. who performed above chance when asked to guess the emotional expressions on a series of faces. To uncover the electrophysiological mechanisms involved in this phenomenon we combined multivariate pattern recognition (MPR) with local field potential estimates provided by electric source imaging (ELECTRA). All faces, including neutral faces, elicited distinctive oscillatory EEG patterns that were correctly identified by the MPR algorithm as belonging to the class of facial expressions actually presented. Consequently, neural responses in this patient are not restricted to emotionally laden faces. Earliest non-specific differences between faces occur from 70 ms onwards in the superior temporal polysensory area (STP). Emotion-specific responses were found after 120 ms in the right anterior areas with right amygdala activation observed only later (∼ 200 ms). Thus, affective blindsight might be mediated by subcortical afferents to temporal areas as suggested in some studies involving non-emotional stimuli. The early activation of the STP in the patient constitutes evidence for fast activation of higher order visual areas in humans despite bilateral V1 destruction. In addition, the absence of awareness of any visual experience in this patient suggests that neither the extrastriate visual areas, nor the prefrontal cortex activation alone are sufficient for conscious perception, which might require recurrent processing within a network of several cerebral areas including V1.

Integration of Bimodal Looming Signals through Neuronal Coherence in the Temporal Lobe

The ability to integrate information across multiple sensory systems offers several behavioral advantages, from quicker reaction times and more accurate responses to better detection and more robust learning. At the neural level, multisensory integration requires large-scale interactions between different brain regions--the convergence of information from separate sensory modalities, represented by distinct neuronal populations. The interactions between these neuronal populations must be fast and flexible, so that behaviorally relevant signals belonging to the same object or event can be immediately integrated and integration of unrelated signals can be prevented. Looming signals are a particular class of signals that are behaviorally relevant for animals and that occur in both the auditory and visual domain. These signals indicate the rapid approach of objects and provide highly salient warning cues about impending impact. We show here that multisensory integration of auditory and visual looming signals may be mediated by functional interactions between auditory cortex and the superior temporal sulcus, two areas involved in integrating behaviorally relevant auditory-visual signals. Audiovisual looming signals elicited increased gamma-band coherence between these areas, relative to unimodal or receding-motion signals. This suggests that the neocortex uses fast, flexible intercortical interactions to mediate multisensory integration.

Touch, sound and vision in human superior temporal sulcus

Human superior temporal sulcus (STS) is thought to be a key brain area for multisensory integration. Many neuroimaging studies have reported integration of auditory and visual information in STS but less is known about the role of STS in integrating other sensory modalities. In macaque STS, the superior temporal polysensory area (STP) responds to somatosensory, auditory and visual stimulation. To determine if human STS contains a similar area, we measured brain responses to somatosensory, auditory and visual stimuli using blood-oxygen level dependent functional magnetic resonance imaging (BOLD fMRI). An area in human posterior STS, STSms (multisensory), responded to stimulation in all three modalities. STSms responded during both active and passive presentation of unisensory somatosensory stimuli and showed larger responses for more intense vs. less intense tactile stimuli, hand vs. foot, and contralateral vs. ipsilateral tactile stimulation. STSms showed responses of similar magnitude for unisensory tactile and auditory stimulation, with an enhanced response to simultaneous auditory–tactile stimulation. We conclude that STSms is important for integrating information from the somatosensory as well as the auditory and visual modalities, and could be the human homolog of macaque STP.

Activation in Posterior Superior Temporal Sulcus Parallels Parameter Inducing the Percept of Animacy

An essential, evolutionarily stable feature of brain function is the detection of animate entities, and one of the main cues to identify them is their movement. We developed a model of a simple interaction between two objects, in which an increase of the correlation between their movements varied the amount of interactivity and animacy observers attributed to them. Functional magnetic resonance imaging revealed that activation in the posterior superior temporal sulcus and gyrus (pSTS/pSTG) increased in relation to the degree of correlated motion between the two objects. This activation increase was not different when subjects performed an explicit or implicit task while observing these interacting objects. These data suggest that the pSTS and pSTG play a role in the automatic identification of animate entities, by responding directly to an objective movement characteristic inducing the percept of animacy, such as the amount of interactivity between two moving objects.

Three-dimensional Structure-from-motion Selectivity in the Anterior Superior Temporal Polysensory Area, STPa, of the Behaving Monkey

Human and non-human primates are able to perceive three-dimensional structure from motion displays. Three-dimensional structure-from-motion (object-motion) displays were used to test the hypothesis that neurons in the anterior division of the superior temporal polysensory area (STPa) of monkeys can selectively respond to three-dimensional structure-from-motion. Monkeys performed a reaction time task that required the detection of a change in the fraction of structure in three-dimensional transparent sphere displays. Neurons were able to distinguish structured and unstructured three-dimensional optic flow. These cells could differentiate the change in structure-from-motion at stimulus presentation and when the animal was detecting the amount of structure in the display. Some of these neurons were also tuned for characteristics of the sphere stimuli. Cells were also tested with navigational motion and many were found to respond both to three-dimensional structure-from-motion and navigational motion. These results suggest that STPa neurons represent specific aspects of three-dimensional surface structure and that neurons within STPa contribute to the perception of three-dimensional structure-from-motion.

Perceptual deficits in patients with impaired recognition of biological motion after temporal lobe lesions

"Biological motion" may be defined by the pattern of movement of a small number of lights attached to the major joints of a human performing simple actions. Normal observers watching such displays immediately recognize a person and his or her actions. In the present study, we investigated the effects of lesions of anterior cortical regions on the perception of biological motion. We measured the performance on psychophysical static and motion tasks and on object and action recognition tests in four stroke patients who presented with a disorder of recognition of biological motion. We relate our results to the finding that neurons in the rostral part of the superior temporal gyrus (the superior temporal polysensory area) respond selectively to biological motion, and to the idea that the superior temporal polysensory area integrates the late stages of the dorsal and ventral cortical visual streams, as well as to recent functional MRI studies on biological motion.

Cell responsiveness in macaque superior temporal polysensory area measured by temporal discriminants.

The firing-rate data from 341 cells from two macaques' superion temporal polysensory area (STPa) were subjected to three different analyses to determine the temporal firing-rate patterns in response to visual optic flow patterns. The data were collected while the monkey viewed four types of optic flow and responded to the change in the display. The mean firing rate (MFR) analysis considered the mean change in firing rate for 500 ms after stimulus onset; the discriminant (DIS) analysis and the principal components (PCA+DIS) analysis considered the change in time-binned firing rate over 1000 ms after stimulus presentation, using bin sizes of 30 to 500 ms. The DIS analysis used a step-down discriminant analysis to find temporal windows in which the cell's firing rate could discriminate among the stimuli; the PCA+DIS analysis extracted the principal components of the cell's firing rates without regard for the stimulus type and then applied a step-down discriminant analysis to the PCA scores to determine whether any of the principal components could discriminate among the stimuli. The two temporal analyses found cells sensitive to the optic flows that the MFR analysis missed. A small proportion of cells showed multiple selectivities under the temporal analyses. Thus, the temporal analyses give a more complete representation of the information encoded by the firing properties of STPa neurons. Finally, this approach incorporates temporal approaches with classical statistical techniques in order to select tuned neurons from a population in an unbiased manner.

The timing and laminar profile of converging inputs to multisensory areas of the macaque neocortex

Two fundamental requirements for multisensory integration are convergence of unisensory (e.g. visual and auditory) inputs and temporal alignment of the neural responses to convergent inputs. We investigated the anatomic mechanisms of multisensory convergence by examining three areas in which convergence occurs, posterior auditory association cortex, superior temporal polysensory area (STP) and ventral intraparietal sulcus area (VIP). The first of these was recently shown to be a site of multisensory convergence and the latter two are more well known as ‘classic’ multisensory regions. In each case, we focused on defining the laminar profile of response to the unisensory inputs. This information is useful because two major types of connection, feedforward and feedback, have characteristic differences in laminar termination patterns, which manifest physiologically. In the same multisensory convergence areas we also examined the timing of the unisensory inputs using the same standardized stimuli across all recordings. Our findings indicate that: (1) like somatosensory input [J. Neurophysiol., 85 (2001) 1322], visual input is available at very early stages of auditory processing, (2) convergence occurs through feedback, as well as feedforward anatomical projections and (3) input timing may be an asset, as well as a constraint in multisensory processing.

Projections from the superior temporal sulcus to the agranular frontal cortex in the macaque.

The aim of this study was to investigate the organization of the projections from the superior temporal sulcus (STS) to the various areas forming the agranular frontal cortex. Injections of retrograde neuronal tracers were made in the various agranular areas, in nine macaque monkeys. The results showed that two rostral premotor areas, F6 (pre-SMA) and F7, and the ventrorostral part of area F2 (F2vr) are targets of projections from the upper bank of the STS (uSTS). F6 and the dorsorostral part of F7 (supplementary eye field, SEF) are targets of projections from the rostral part of the uSTS, corresponding to the so-called 'superior temporal polysensory area' (STP). In contrast, the ventral part of area F7 (not including the SEF) and F2vr are targets of afferents from the caudal part of the uSTS. Ventral F7 is the target of weak afferents from the caudalmost and dorsalmost part of the uSTS (area 7a), whilst F2vr is the target of projections from a relatively more rostral and ventral sector of the uSTS, close to the fundus of the sulcus. This sector should correspond to area MST. In conclusion, F6 and SEF receive high order information from STP, whereas ventral F7 and F2vr receive information from areas of the dorsal visual stream.

Interlaminar differences in the pyramidal cell phenotype in cortical areas 7 m and STP (the superior temporal polysensory area) of the macaque monkey.

Pyramidal neurones were injected with Lucifer Yellow in slices cut tangential to the surface of area 7 m and the superior temporal polysensory area (STP) of the macaque monkey. Comparison of the basal dendritic arbors of supra- and infragranular pyramidal neurones (n = 139) that were injected in the same putative modules in the different cortical areas revealed variation in their structure. Moreover, there were relative differences in dendritic morphology of supra- and infragranular pyramidal neurones in the two cortical areas. Sholl analyses revealed that layer III pyramidal neurones in area STP had considerably higher peak complexity (maximum number of dendritic intersections per Sholl circle) than those in layer V, whereas peak complexities were similar for supra- and infragranular pyramidal neurones in area 7 m. In both cortical areas, the basal dendritic trees of layer III pyramidal neurones were characterized by a higher spine density than those in layer V. Calculations of the total number of dendritic spines in the "average" basal dendritic arbor revealed that layer V pyramidal neurones in area 7 m had twice as many spines as cells in layer III (4535 and 2294, respectively). A similar calculation for neurones in area STP revealed that layer III pyramidal neurones had approximately the same number of spines as cells in layer V (3585 and 3850 spines, respectively). Relative differences in the branching patterns of, and the number of spines in, the basal dendritic arbors of supra- and infragranular pyramidal neurones in the different cortical areas may allow for integration of different numbers of inputs, and different degrees of dendritic processing. These results support the thesis that intra-areal circuitry differs in different cortical areas.

Pyramidal Cells, Patches, and Cortical Columns: a Comparative Study of Infragranular Neurons in TEO, TE, and the Superior Temporal Polysensory Area of the Macaque Monkey

The basal dendritic arbors of layer III pyramidal neurons are known to vary systematically among primate visual areas. Generally, those in areas associated with "higher" level cortical processing have larger and more spinous dendritic arbors, which may be an important factor for determining function within these areas. Moreover, the tangential area of their arbors are proportional to those of the periodic supragranular patches of intrinsic connections in many different areas. The morphological parameters of both dendritic and axon arbors may be important for the sampling strategies of cells in different cortical areas. However, in visual cortex, intrinsic patches are a feature of supragranular cortex, and are weaker or nonexistent in infragranular cortex. Thus, the systematic variation in the dendritic arbors of pyramidal cells in supragranular cortex may reflect intrinsic axon projections, rather than differences in columnar organization. The present study was aimed at establishing whether cells in the infragranular layers also vary in terms of dendritic morphology among different cortical areas, and whether these variations mirror the ones demonstrated in supragranular cortex. Layer V pyramidal neurons were injected with Lucifer yellow in flat-mounted cortical slices taken from cytoarchitectonic areas TEO and TE and the superior polysensory area (STP) of the macaque monkey. The results demonstrate that cells in STP were larger, had more bifurcations, and were more spinous than those in TE, which in turn were larger, had more bifurcations and were more spinous than those in TEO. These results parallel morphological variation seen in layer III pyramidal neurons, suggesting that increasing complexity of basal dendritic arbors of cells, with progression through higher areas of the temporal lobe, is a general organizational principle. It is proposed that the differences in microcircuitry may contribute to the determination of the functional signatures of neurons in different cortical areas. Furthermore, these results provide evidence that intrinsic circuitry differs across cortical areas, which may be important for theories of columnar processing.

Connections between Anterior Inferotemporal Cortex and Superior Temporal Sulcus Regions in the Macaque Monkey

We examined the connections between the anterior inferotemporal cortex and the superior temporal sulcus (STS) in the macaque monkey by injecting Phaseolus vulgaris leucoagglutinin (PHA-L) or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the dorsoanterior and ventroanterior subdivisions of TE (TEad and TEav, respectively) and observing the labeled terminals and cell bodies in STS. We found a clear dichotomy in the connections of the rostral part of STS: the injections into TEad resulted in a dense distribution of labeled terminals and cell bodies in the upper bank of rostral STS, whereas labeling was confined to the lower bank and fundus of rostral STS after injections into TEav. The distribution of labeling in the rostral STS was discontinuous from the distribution of labeling surrounding the injection sites: the lower bank of the rostral STS was spared from labeling in the TEad injection cases, and TEad had only sparse distribution in the TEav injection cases. These results revise the classical view that the lower bank of rostral STS is connected with TE, whereas the upper bank of rostral STS is connected with the parietal, prefrontal, and superior temporal regions (Seltzer and Pandya, 1978, 1991, 1994). The upper bank of the rostral STS is called the superior temporal polysensory area (STP), because it was previously found that neurons there respond to auditory, somatosensory, and visual stimuli. The present results thus suggest that the polymodal representation in STP interacts more with information processing in TEad than TEav. It is also suggested that the information processing in the ventral bank of the rostral STS is distinct from that in TEad, and the former more directly interacts with TEav than TEad.

Cortical integration in the visual system of the macaque monkey: large-scale morphological differences in the pyramidal neurons in the occipital, parietal and temporal lobes.

Layer III pyramidal neurons were injected with Lucifer yellow in tangential cortical slices taken from the inferior temporal cortex (area TE) and the superior temporal polysensory (STP) area of the macaque monkey. Basal dendritic field areas of layer III pyramidal neurons in area STP are significantly larger, and their dendritic arborizations more complex, than those of cells in area TE. Moreover, the dendritic fields of layer III pyramidal neurons in both STP and TE are many times larger and more complex than those in areas forming 'lower' stages in cortical visual processing, such as the first (V1), second (V2), fourth (V4) and middle temporal (MT) visual areas. By combining data on spine density with those of Sholl analyses, we were able to estimate the average number of spines in the basal dendritic field of layer III pyramidal neurons in each area. These calculations revealed a 13-fold difference in the number of spines in the basal dendritic field between areas STP and V1 in animals of similar age. The large differences in complexity of the same kind of neuron in different visual areas go against arguments for isopotentiality of different cortical regions and provide a basis that allows pyramidal neurons in temporal areas TE and STP to integrate more inputs than neurons in more caudal visual areas.

Decision-related activity in the macaque dorsal visual pathway.

Brain areas at higher levels of cortical organization are thought to be more involved in decision processes than are earlier, i.e. lower, sensory areas. Hence, neuronal activity correlated with decisions should vary with an area's position in the cortical hierarchy. To test this proposal, we investigated whether a change in neuronal activity during error trials depends in a systematic way on cortical hierarchical position. While macaque monkeys discriminated the direction of moving visual stimuli, the activity of direction-selective neurons was recorded in four extrastriate visual areas: V3A, the middle temporal area, the middle superior temporal area and the posterior part of the superior temporal polysensory area. Neuronal activity was significantly reduced in all areas when the monkeys made errors in judging the direction of stimuli moving in the preferred direction with low and intermediate luminance contrast. The amount of activity reduction was approximately 50% in all of the visual areas. Thus, the activity on error trials is reduced in early visual processing, independent of the hierarchy in the dorsal visual pathway. The activity reduction depended on stimulus contrast and the direction of the decision relative to the stimulus motion. It was profound and significant in all areas at low stimulus contrast. However, it was nonsignificant at high stimulus contrast. Our data suggest that activity reduction on error trials is due to lack of attention in association with stimulus expectation.