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The Journal of Neuroscience, April 8, 2009, 29(14):4381-4391; doi:10.1523/JNEUROSCI.0377-09.2009

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Behavioral/Systems/Cognitive
Is That within Reach? fMRI Reveals That the Human Superior Parieto-Occipital Cortex Encodes Objects Reachable by the Hand

Jason P. Gallivan,¹ Cristiana Cavina-Pratesi,³ and Jody C. Culham^1,2

¹Neuroscience Program and ²Department of Psychology, University of Western Ontario, London, Ontario, Canada N6A 5C2, and ³Department of Psychology, Durham University, Durham DH1 3LE, United Kingdom

Correspondence should be addressed to Jody C. Culham, Department of Psychology, University of Western Ontario, London, Ontario, Canada N6A 5C2. Email: jculham{at}uwo.ca

Macaque neurophysiology and human neuropsychology results suggest that parietal cortex encodes a unique representation of space within reach of the arm. Here, we used slow event-related functional magnetic resonance imaging (fMRI) to investigate whether human brain areas involved in reaching are more activated by objects within reach versus beyond reach. In experiment 1, graspable objects were placed at three possible locations on a platform: two reachable locations and one beyond reach. On some trials, participants reached to touch or grasp objects at the reachable location; on other trials participants passively viewed objects at one of the three locations. A reach-related area in the superior parieto-occipital cortex (SPOC) was more activated for targets within reach than beyond. In experiment 2, we investigated whether this SPOC response occurred when visual and motor confounds were controlled and whether it was modulated when a tool extended the effective range of the arm. On some trials, participants performed grasping and reaching actions to a reachable object location using either the hand alone or a tool; on other trials, participants passively viewed reachable and unreachable object locations. SPOC was significantly more active for passively viewed objects within reach of the hand versus beyond reach, regardless of whether or not a tool was available. Interestingly, these findings suggest that neural responses within brain areas coding actions (such as SPOC for reaching) may reflect automatic processing of motor affordances (such as reachability with the hand).

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Received Jan. 23, 2009; revised Feb. 24, 2009; accepted Feb. 27, 2009.

Correspondence should be addressed to Jody C. Culham, Department of Psychology, University of Western Ontario, London, Ontario, Canada N6A 5C2. Email: jculham{at}uwo.ca

This article has been cited by other articles:

				J. P. Gallivan and D. K. Wood Simultaneous Encoding of Potential Grasping Movements in Macaque Anterior Intraparietal Area J. Neurosci., September 30, 2009; 29(39): 12031 - 12032. [Full Text] [PDF]

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