Cortical activation to object shape and speed of motion during the first year

Abstract

A great deal is known about the functional organization of cortical networks that mediate visual object processing in the adult. The current research is part of a growing effort to identify the functional maturation of these pathways in the developing brain. The current research used near-infrared spectroscopy to investigate functional activation of the infant cortex during the processing of featural information (shape) and spatiotemporal information (speed of motion) during the first year of life. Our investigation focused on two areas that were implicated in previous studies: anterior temporal cortex and posterior parietal cortex. Neuroimaging data were collected with 207 infants across three age groups: 3-6 months (Experiment 1), 7-8 months (Experiment 2), and 10-12 months (Experiments 3 and 4). The neuroimaging data revealed age-related changes in patterns of activation to shape and speed information, mostly involving posterior parietal areas, some of which were predicted and others that were not. We suggest that these changes reflect age-related differences in the perceptual and/or cognitive processes engaged during the task.

Keywords: Functional brain activation; Infants; Near-infrared spectroscopy; Object processing; Parietal cortex; Temporal cortex.

Figure 1

The shape difference, color difference, and control test events of Wilcox et al. (2012). Each cycle of the test event was 10 s and infants saw 2 complete cycles during each test trial.

Figure 2

The speed-discontinuity, path-discontinuity, and control test events of Wilcox et al. (2010). Each cycle of the test event was 12 s and infants saw 2 complete cycles during each test trial. These are also the test events used in Experiment 4.

Figure 3

The shape difference, speed discontinuity, and control test events of Experiments 1 to 3. Each cycle of the test event was 12 s and infants saw 2 complete cycles during each test trial.

Figure 4

Configuration and placement of optodes. (a) Location of emitters (large red circles) and detectors (black squares) on the infant’s head in relation to the 10–20 International EEG system (small black circles). This configuration was identical to that used by Wilcox et al. (2010, . Also represented are the nine corresponding channels from which data were collected. Each detector read from a single emitter except for the detector between T3 and T5, which read from both emitters. The light was frequency modulated to prevent “cross-talk”. (b) Configuration of the emitters (red circles) and detectors (black squares), and the nine channels, in the headgear. Emitter-detector distances were all 2 cm. (c) Infants sat in a supportive seat to restrain excess movement. An elasticized headband was slid onto the infant’s head and secured by a chinstrap.

Figure 5

Hemodynamic response curves for Experiments 1 to 3 (smoothed for presentation purposes with a 0.5 Hz low-pass filter). Relative changes in HbO and HbR (red and blue lines respectively) during each test event at each of the nine channels are displayed for each of the three experiments, separately. Time is on the x-axis and hemodynamic changes in μM cm on the y-axis. The bold lines separate channels associated with each of the four 10–20 coordinates. In all three experiments, 1 to 24 s was the test event and 25 to 34 s was the silent pause (baseline). The hemodynamic response was averaged over 7 to 24 s, indicated by narrow grey shading. Our analyses focused on channels 2, 3, 6, and 7, as indicated by wide grey panels. Asterisks indicate M (SD) responses that differed significantly from baseline (* p < .05, ** p < .01, *** p < .001).

Figure 6

Patterns of neural activation obtained for the 3- to 6-month-olds (Experiment 1), 7- to 8-month-olds (Experiment 2), and 10- to 12-month-olds (Experiment 3). The colored dots (large green = shape difference, medium blue = speed discontinuity, small yellow = control) indicate that neural activation was obtained during that test event at that channel. The distance between sources and detectors remained fixed but mean head size varied by age (see text). The black lines indicate the actual location of T3, T5, and P3 (based on mean head measurements) for the younger and older infants.

Figure 7

Hemodynamic response curves for Experiment 4 (smoothed for presentation purposes with a 0.5 Hz low-pass filter). Relative changes in HbO and HbR (red and blue lines respectively) during each test event at each of the nine channels are displayed. Time is on the x-axis and hemodynamic changes in μM cm on the y-axis. The bold lines separate channels associated with each of the four 10–20 coordinates. Time 1 to 24 s was the test event and 25 to 34 s was the silent pause (baseline). The hemodynamic response was averaged over 7 to 24 s, indicated by narrow grey shading. Our analyses focused on channels 2, 3, 6, and 7, as indicated by wide grey panels. Asterisks indicate M (SD) responses that differed significantly from baseline (* p < .05, ** p < .01, *** p < .001).