Authors:

MITCHELL, D., DUNCAN, J. & CUSACK, R.

Reference:

Year of publication:

2006

CBU number:

6308

Abstract:

Objective: The intraparietal sulcus (IPS) is part of a fronto-parietal network activated, across a diverse range of tasks, as difficulty increases or when there is an increased demand for attentional control [e.g. 1-3]. Being part of the dorsal visual pathway and receiving auditory and somatosensory input, it is also well positioned to process and integrate high-level perceptual information and has been shown to respond to the presence and number of visual objects and perceived auditory streams, even in the absence of any obvious difficulty or attentional components [2,5]. We aimed to investigate, using functional MRI, the extent to which these functions of the IPS could be differentiated within a single experiment. Methods: BOLD activity was measured while sixteen volunteers were scanned at 3T. They performed a task that involved monitoring of superimposed, oscillating dot surfaces for transient target displacements (fig. 1). Perceptual salience of targets, number of surfaces, and requirement for switching attention between surfaces, were varied across conditions. Using a random effects analysis under the general linear model, whole-brain SPM t-maps were generated for the primary contrasts (2 > 1 surface; switching > focused attention) and an overlap map was calculated showing the ratio of the t-values (fig. 2). Regions of interest (ROIs) were defined in the IPS that reflect general executive control [tasks from 4] and object processing [5], in order to test whether they responded differentially. Results & Discussion: As expected, both the attention-related and object-related contrasts activated a fronto-parietal network, including the IPS and superior parietal lobule. However, ROI analyses revealed a significant region-by-contrast interaction within the predefined ROIs. Conclusions: Although a range of different processes activate largely similar regions in and around the IPS, it is possible to differentiate visual object processing from more general executive processes in this region. References: [1] Lee KH et al. (2005) Neural correlates of superior intelligence: stronger recruitment of posterior parietal cortex. NeuroImage. [In press] [2] Cusack R (2005) The Intraparietal Sulcus and Perceptual Organization. J. Cogn Neurosci. 17(4): 641-651 [3] Wojciulik E and Kanwisher N (1999) The generality of parietal involvement in visual attention. Neuron 23:747-764 [4] Duncan J and Owen AM (2000) Common regions of the human frontal lobe recruited by diverse cognitive demands. Trends Neurosci. 23(10):475-83 [5] Fang F and He S (2005) Cortical responses to invisible objects in the human dorsal and ventral pathways. Nat Neurosci. 8(10):1380-5