The minimum effective shape feature for neurons in the macaque Anterior Intraparietal area
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1
KULeuven, Laboratory for Neuro- and Psychofysiology, Belgium
Neurons in the Anterior Intraparietal area (AIP) respond selectively to two-dimensional shapes and contours (Romero et al., 2012). In the present study we investigated the minimum effective shape features evoking selective responses in AIP of two rhesus monkeys using a stimulus reduction approach. The stimulus set in this reduction test consisted of contour shapes derived from images of real-world objects (full outlines; circumference ~16 deg), and line segments obtained by subdividing the full contours into 4, 8 and 16 segments (length 4, 2 and 1 deg, respectively). We first mapped the receptive field (RF) of every responsive AIP neuron with effective (preferred) and non-effective (nonpreferred) images of real-world objects (size 3 deg) presented in a 12 by 8 deg area around the fixation point during passive fixation. All stimuli in the reduction test were presented on the RF center, at their corresponding position in the original image. Almost all AIP neurons tested (47/48) responded significantly to at least one of the 4, 8 or 16-fragment stimuli obtained by reduction. We considered that a shape fragment was effective for the neuron if the response rate to the fragment was at least 50 % of their maximum response in the test. With this criterion, 83% (40/48) of our AIP cells responded to at least one of the 4-fragment stimuli, 88% (42/48) responded to at least one of the 8-fragment stimuli, and 75% (36/48) responded to at least one of the 16- fragment stimuli. However, the number of effective fragments for each cell was on average low, as most neurons (41/ 48; 85 %) were only responsive for less than 6 fragments in the test. A large majority of cells (41/48; 88%) responding to fragments in the preferred shape were also responsive to fragments derived from the nonpreferred shape. The RF mapping revealed a cluttered RF profile in a high proportion of AIP cells (33/48; 69%), with several local maxima and minima. Furthermore, the RF profile depended heavily on the stimulus used, as measured by the low 2D correlation between responses to the best 3 deg surface and the best fragment (average r = 0.36). The remaining AIP cells (15/48; 31%) showed localized, foveal RFs. Overall, our results demonstrate that for most AIP neurons the minimum effective shape feature consists of very small line fragments measuring merely 1 deg. The RF structure in AIP can be highly complex and depending on the stimulus used.
Acknowledgements
Supported by ERC-StG-260607, PFV10 ⁄ 008, GOA 10 ⁄ 19, FWO (G.0713.09).
References
Romero M.C., Van Dromme I., Janssen P. (2012) Responses to two-dimensional shapes in the macaque anterior intraparietal area. European Journal of Neuroscience, 36: 2324-2334.
Keywords:
Visual Neuroscience,
shape,
Parietal Lobe,
Electrophysiology,
monkey
Conference:
Belgian Brain Council, Liège, Belgium, 27 Oct - 27 Oct, 2012.
Presentation Type:
Poster Presentation
Topic:
Other basic/clinical neurosciences topic
Citation:
Romero
MC and
Janssen
P
(2012). The minimum effective shape feature for neurons in the macaque Anterior Intraparietal area.
Conference Abstract:
Belgian Brain Council.
doi: 10.3389/conf.fnhum.2012.210.00109
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Received:
21 Aug 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Dr. Maria C Romero, KULeuven, Laboratory for Neuro- and Psychofysiology, Leuven, 3000, Belgium, Maria.C.Romero@med.kuleuven.be
Prof. Peter Janssen, KULeuven, Laboratory for Neuro- and Psychofysiology, Leuven, 3000, Belgium, Peter.Janssen@med.kuleuven.be