We studied the corticocortical connections of architectonically defined areas of parietal and temporoparietal cortex, with emphasis on areas in the intraparietal sulcus (IPS) that are implicated in visual and somatosensory integration. Retrograde tracers were injected into selected areas of the IPS, superior temporal sulcus, and parietal lobule. The distribution of labeled cells was charted in relation to architectonically defined borders throughout the hemisphere and displayed on computer-generated three-dimensional reconstructions and on cortical flat maps. Injections centered in the ventral intraparietal area (VIP) revealed a complex pattern of inputs from numerous visual, somatosensory, motor, and polysensory areas, and from presumed vestibular- and auditory-related areas. Sensorimotor projections were predominantly from the upper body representations of at least six somatotopically organized areas. In contrast, injections centered in the neighboring ventral lateral intraparietal area (LIPv) revealed inputs mainly from extrastriate visual areas, consistent with previous studies. The pattern of inputs to LIPv largely overlapped those to zone MSTdp, a newly described subdivision of the medial superior temporal area. These results, in conjunction with those from injections into other parietal areas (7a, 7b, and anterior intraparietal area), support the fine-grained architectonic partitioning of cortical areas described in the preceding study. They also support and extend previous evidence for multiple distributed networks that are implicated in multimodal integration, especially with regard to area VIP.

The intraparietal sulcus (IPS) of the macaque monkey contains numerous areas associated with different aspects of cortical function, including motor control as well as visual, somatosensory, vestibular, and possibly auditory processing. This study focuses largely on the architectonic organization of areas within and near the IPS, but also examines remaining portions of the hemisphere with which the IPS is interconnected. We charted the location of up to 72 architectonically distinct areas plus numerous architectonic zones in individuals over a region covering most of the cortical hemisphere. Identified cortical subdivisions (areas plus zones) were represented on computationally generated flat maps in relation to gyral and sulcal geography, thereby facilitating the analysis of consistent as well as variable aspects of the sizes and relative positions of subdivisions across animals. Using myelin and Nissl stains, plus immunohistochemical staining with the SMI-32 antibody, 17 architectonic subdivisions were identified that are largely or entirely contained in the intraparietal and parieto-occipital sulci. This includes four newly identified zones: a heavily myelinated lateral occipitoparietal zone, termed LOP; a strongly SMI-32 immunoreactive zone termed 7t (near the tip of the IPS); plus medial and lateral subdivisions (VIPm and VIPl) of ventral intraparietal area (VIP), which was previously regarded as an anatomically homogeneous area. Within the superior temporal sulcus, we identified a densely myelinated zone termed the dorso-posterior subdivision of the medial superior temporal area (MSTdp) that bordered middle temporal area (MT). We charted the extent of numerous other architectonically defined subdivisions throughout the cortical hemisphere by using criteria largely based on previous studies, but in some instances involving revised or expanded identification criteria.

Greater manual dexterity and greater conceptual knowledge of tool use represent two main features that distinguish humans from other primates. Studies of human brain lesions suggest that the left hemisphere (at least in right-handed people) includes a system for processing manual skills that is specialized for tool use that interacts with another system involved more with conceptualizing, planning, and accessing knowledge associated with tool use. Growing evidence from recent neuroimaging studies supports this organization, and studies have begun to highlight specific brain regions and pathways that may be necessary for tool use. This review compares and summarizes results from 64 paradigms published over the past decade that have examined cortical regions associated with tool use skills and tool knowledge. A meta-analysis revealed cortical networks in both hemispheres, though with a clear left hemisphere bias, which may be organized to optimally represent action knowledge. Portions of this network appear to represent part of a system that is tightly linked with language systems, which is discussed together with the effects that handedness may have on the cortical organization for tool use.

Human listeners can effortlessly categorize a wide range of environmental sounds. Whereas categorizing visual object classes (e.g., faces, tools, houses, etc.) preferentially activates different regions of visually sensitive cortex, it is not known whether the auditory system exhibits a similar organization for different types or categories of complex sounds outside of human speech. Using functional magnetic resonance imaging, we show that hearing and correctly or incorrectly categorizing animal vocalizations (as opposed to handmanipulated tool sounds) preferentially activated middle portions of the left and right superior temporal gyri (mSTG). On average, the vocalization sounds had much greater harmonic and phase-coupling content (acoustically similar to human speech sounds), which may represent some of the signal attributes that preferentially activate the mSTG regions. In contrast, correctly categorized tool sounds (and even animal sounds that were miscategorized as being tool-related sounds) preferentially activated a widespread, predominantly left hemisphere cortical "mirror network." This network directly overlapped substantial portions of motor-related cortices that were independently activated when participants pantomimed tool manipulations with their right (dominant) hand. These data suggest that the recognition processing for some sounds involves a causal reasoning mechanism (a high-level auditory "how" pathway), automatically evoked when attending to hand-manipulated tool sounds, that effectively associates the dynamic motor actions likely to have produced the sound(s).

We have used surface-based atlases of the cerebral cortex to analyze the functional organization of visual cortex in humans and macaque monkeys. The macaque atlas contains multiple partitioning schemes for visual cortex, including a probabilistic atlas of visual areas derived from a recent architectonic study, plus summary schemes that reflect a combination of physiological and anatomical evidence. The human atlas includes a probabilistic map of eight topographically organized visual areas recently mapped using functional MRI. To facilitate comparisons between species, we used surface-based warping to bring functional and geographic landmarks on the macaque map into register with corresponding landmarks on the human map. The results suggest that extrastriate visual cortex outside the known topographically organized areas is dramatically expanded in human compared to macaque cortex, particularly in the parietal lobe.