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Behavioral studies have suggested that food cues have stronger motivating effects in obese than in normal-weight individuals, which may be a risk factor underlying obesity. Previous cross-sectional neuroimaging studies have suggested that this difference is mediated by increased reactivity to food cues in parts of the reward system in obese individuals. To date, however, only a few prospective neuroimaging studies have been conducted to examine whether individual differences in brain activation elicited by food cues can predict differences in weight change. We used functional magnetic resonance imaging (fMRI) to investigate activation in reward-system as well as other brain regions in response to viewing high-calorie food vs. control pictures in 25 obese individuals before and after a 12-week psychosocial weight-loss treatment and at 9-mo follow-up. In those obese individuals who were least successful in losing weight during the treatment, we found greater pre-treatment activation to high-calorie food vs. control pictures in brain regions implicated in reward-system processes, such as the nucleus accumbens, anterior cingulate, and insula. We found similar correlations with weight loss in brain regions implicated by other studies in vision and attention, such as superior occipital cortex, inferior and superior parietal lobule, and prefrontal cortex. Furthermore, less successful weight maintenance at 9-mo follow-up was predicted by greater post-treatment activation in such brain regions as insula, ventral tegmental area, putamen, and fusiform gyrus. In summary, we found that greater activation in brain regions mediating motivational and attentional salience of food cues in obese individuals at the start of a weight-loss program was predictive of less success in the program and that such activation following the program predicted poorer weight control over a 9-mo follow-up period.

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The latencies and visual response properties of 202 X-cells in the A-laminae of the cat dorsal lateral geniculate nucleus (LGN) were examined to investigate the recent claim (Mastronarde, '85,'87a) that functionally different groups of X-cells reside there. Two groups of X-cells were found, which differed in their extracellularly recorded responses to spots of light flashed within their receptive fields. One group, constituting one-third of the sample, responded to spot onset with a profound and often long-lasting dip in discharge rate, such that cell discharge usually did not reach half maximum until greater than or equal to 100 msec after spot onset. About 70% of these cells also displayed a transient discharge at spot onset. These cells correspond to Mastronarde's lagged X-cells, and we similarly refer to them as XL-cells. The second group, constituting the remainder of the X-cell population, generally responded to spot onset with a short latency (less than or equal to 60 msec) brisk discharge, no detectable XL-type dip, and a rapid reduction in firing at spot offset. We refer to these neurons as nonlagged (XN) X-cells; this group probably encompasses all of Mastronarde's non-XL-cells. Despite some overlap, the XL- and XN-cells differed in numerous other features. Compared to XN-cells, XL-cells exhibited: 1) lower peak rates of discharge and more uniform firing during spot onset; 2) slightly longer latencies and markedly lower probabilities of discharge to optic chiasm stimulation; 3) consistently lower geniculocortical conduction velocities; and 4) markedly lower optimal temporal frequencies when tested with drifting sine wave gratings. No differences were found between the two cell groups in optimal spatial frequency, spatial resolution, or receptive field center size, and there were equal proportions of on- and off-center types of XL- and XN-cells. Analyses of one- and two-dimensional plots of the physiological measures indicate that XL- and XN-cells constitute a physiological continuum. However, the two groups occupy opposite sides of the continuum on many of the measures, with little overlap and with few (less than 5%) cells with intermediate properties. Therefore, XL-cells may be considered a distinct, readily identifiable group. These findings confirm and extend Mastronarde's ('87a) observations on functional differences among geniculate X-cells.(ABSTRACT TRUNCATED AT 400 WORDS)