Prolonged masking effects after frontal cortex lesions

Prolonged masking effects after frontal cortex lesions

Brain and Cognition 46, 12-15 (2001) doi:10.1006/brcg.2000.1267, available online at http://www.idealibrary.com on InE~L ® ABSTRACTS Frontal Slowing...

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Brain and Cognition 46, 12-15 (2001) doi:10.1006/brcg.2000.1267, available online at http://www.idealibrary.com on

InE~L ®

ABSTRACTS Frontal Slowing Is"Not Due to a Lower Preparation Rate. Sylvain Brdard, M~lanie Renaud, and Francois Richer, Universit~ du Quebec, Montrral, Canada. Frontal brain lesions affect the speed of response programming and initiation (akinesia and bradykinesia) but the underlying mechanisms of this problem are still unknown. One hypothesis is that frontal lesions perturb the rate of preparation of responses. We tested this idea by comparing seven patients with unilateral frontal lesions, seven patients with temporal lesions, and seven controls in a rapid decision task in which the response selection cue was provided shortly before the signal to respond. Subjects executed one of two keypress sequences (index then middle finger or the opposite) depending on a spatial cue (100-ms change of color on left or right). The preparatory interval (1.5 s) was cued by a moving line on a screen and the signal to respond was a tone which occurred at the time the moving line reached a stationary line. The spatial cue occurred 200, 380, or 560 ms before the response signal. The frontal group showed longer response times than the other groups. Response time decreased with the preparatory delay in all groups but there was no difference in the slope of this decrease in the three groups. This suggests that the slowing after frontal lesions cannot be explained by a general problem in response preparation rate and that other portions such as baseline preparation or final postimperative programming must contribute to slowing.

Sleep and Spatial Learning in Humans. Sylvie Chouinard,* lsabelle Beaulieu,* Constant Rainville,? and Roger Godbout,* *Centre de recherche Fernand-Seguin, H6pital Louis-H. Lafontaine & Drpartement de psychiatrie, Universit~ de Montr6al; and ?Centre de recherche, Institut de grriatrie de Montrral. Several reports have shown a relation between sleep and cognitive processes but none have focused on spatial memory. The sleep of 22 control participants was recorded in a sleep laboratory while 10 others were sleep deprived. The next morning all participants were tested in a human-size maze where they had to learn three different routes of increasing difficulty. Correlation between sleep parameters and maze performance was calculated. There was a positive correlation between the number of sleep spindle per hour of stage 2 in the last third of the night and: (a) number of errors; and (b) time taken to carry out the routes. Sleep-deprived subjects performed at the same level as control participants. This suggests a carry over effect of sleep maintenance mechanisms on spatial performance.

Prolonged Masking Effects after Frontal Cortex Lesions. Genevieve Maheu & Francois Richer, Centre de Neuroscience de la Cognition, Universit6 du Quebec ~t Montreal. Frontal brain lesions are not often associated with perceptual deficits. However, recent neurophysiological data suggest that frontal neural activity is associated with perceptual decisions on masked stimuli (Thompson & Schall, 1999). We examined whether frontal excisions in man increased susceptibility to backward masking in rapid stimulus streams. Patients with unilateral frontal excisions were compared to controls in the detection of brief (16 ms) single white letters embedded in short streams of eight black letters in three presentation conditions (30 trials per condition): (a) an 80-ms delay between adjacent letters; (b) an 80-ms delay between letters with the omission of the first posttarget mask (masking delay of 160 ms); and (c) a 110-ms delay between letters. Patients with frontal lesions showed much higher error rates in target detection at both presentation rates but not when the mask was removed. As expected, a majority of errors involved reporting the posttarget mask instead of the target. Also, the response time to correct target detections was longer at the short masking delay. The data suggest that perceptual decisions have a prolonged susceptibility to perturbation after frontal lesions.

Sex Differences in Relative Index and Ring Finger Length. M. Peters,* U. Tan,? K. MacKenzie, and P. Bryden. *Department of Psychology, University of Guelph, Guelph, Ontario, Canada NIG 2WI; ?Department of Physiology, Black Sea Technical University, Trabzon, Turkey. Eckert (1875) observed an asymmetry between index and ring finger length, such that the ring finger was shorter than the index finger--as measured against the middle finger. He stated that this was the 12 0278-2626/01 $35.00 Copyright © 2001 by Academic Press All rights of reproduction in any form reserved.