Gesturing tool use and tool transport actions modulates inferior parietal functional connectivity with the dorsal and ventral object processing pathways.

Interacting with manipulable objects (tools) requires the integration of diverse computations supported by anatomically remote regions. Previous functional neuroimaging research has demonstrated the left supramarginal (SMG) exhibits functional connectivity to both ventral and dorsal pathways, supporting the integration of ventrally-mediated tool properties and conceptual knowledge with dorsally-computed volumetric and structural representations of tools. This architecture affords us the opportunity to test whether interactions between the left SMG, ventral visual pathway, and dorsal visual pathway are differentially modulated when participants plan and generate tool-directed gestures emphasizing functional manipulation (tool use gesturing) or structure-based grasping (tool transport gesturing). We found that functional connectivity between the left SMG, ventral temporal cortex (bilateral fusiform gyri), and dorsal visual pathway (left superior parietal lobule/posterior intraparietal sulcus) was maximal for tool transport planning and gesturing, whereas functional connectivity between the left SMG, left ventral anterior temporal lobe, and left frontal operculum was maximal for tool use planning and gesturing. These results demonstrate that functional connectivity to the left SMG is differentially modulated by tool use and tool transport gesturing, suggesting that distinct tool features computed by the two object processing pathways are integrated in the parietal lobe in the service of tool-directed action.

Fast periodic visual stimulation to study tool-selective processing in the human brain.

Because tools are manipulated for the purpose of action, they are often considered to be a specific object category that associates perceptual and motor properties. Their neural processing has been studied extensively by comparing the cortical activity elicited by the separate presentation of tool and non-tool objects, assuming that observed differences are solely due to activity selective for processing tools. Here, using a fast periodic visual stimulation (FPVS) paradigm, we isolated EEG activity selectively related to the processing of tool objects embedded in a stream of non-tool objects. Participants saw a continuous sequence of tool and non-tool images at a 3.7 Hz presentation rate, arranged as a repeating pattern of four non-tool images followed by one tool image. We expected the stimulation to generate an EEG response at the frequency of image presentation (3.7 Hz) and its harmonics, reflecting activity common to the processing of tool and non-tool images. Most importantly, if tool and non-tool images evoked different neural responses, we expected this differential activity to generate an additional response at the frequency of tool images (3.7 Hz/5 = 0.74 Hz). To ensure that this response was not due to unaccounted for systematic differences in low-level visual features, we also tested a phase-scrambled version of the sequence. The periodic insertion of tool stimuli within a stream of non-tool stimuli elicited a significant EEG response at the tool-selective frequency and its harmonics. This response was reduced when the images were phase-scrambled. We conclude that FPVS is a promising technique to selectively measure tool-related activity.

The Neural Bases of Event Monitoring across Domains: a Simultaneous ERP-fMRI Study.

The ability to check and evaluate the environment over time with the aim to detect the occurrence of target stimuli is supported by sustained/tonic as well as transient/phasic control processes, which overall might be referred to as event monitoring. The neural underpinning of sustained attentional control processes involves a fronto-parietal network. However, it has not been well-defined yet whether this cortical circuit acts irrespective of the specific material to be monitored and whether this mediates sustained as well as transient monitoring processes. In the current study, the functional activity of brain during an event monitoring task was investigated and compared between two cognitive domains, whose processing is mediated by differently lateralized areas. Namely, participants were asked to monitor sequences of either faces (supported by right-hemisphere regions) or tools (left-hemisphere). In order to disentangle sustained from transient components of monitoring, a simultaneous EEG-fMRI technique was adopted within a block design. When contrasting monitoring versus control blocks, the conventional fMRI analysis revealed the sustained involvement of bilateral fronto-parietal regions, in both task domains. Event-related potentials (ERPs) showed a more positive amplitude over frontal sites in monitoring compared to control blocks, providing evidence of a transient monitoring component. The joint ERP-fMRI analysis showed that, in the case of face monitoring, this transient component relies on right-lateralized areas, including the inferior parietal lobule and the middle frontal gyrus. In the case of tools, no fronto-parietal areas correlated with the transient ERP activity, suggesting that in this domain phasic monitoring processes were masked by tonic ones. Overall, the present findings highlight the role of bilateral fronto-parietal regions in sustained monitoring, independently of the specific task requirements, and suggest that right-lateralized areas subtend transient monitoring processes, at least in some task contexts.