The influence of deviant behavior on inhibitory gating measures in schizophrenic patients

Schizophrenia patients exhibit inhibitory gating deficit in the prepulse inhibition (PPI) of acoustic startle response (ASR) and in the P50 auditory evoked potential suppression.Deviant sexual behavior (DSB) often complicates early clinical identifying of schizophrenic disorder. In this study we assessed the inhibitory gating measures in schizophrenic patients with DSB.Participants (males) were 12 schizophrenic patients with DSB, 14 schizophrenic controls (SC) and 26 healthy controls (HC). DSB was mainly related to disorders of sexual preference. P50 suppression was measured during two runs of 50 click pairs with 500-msec interval. PPI was measured using a series of prepulse-pulse pairs with lead intervals (LI) 60 ms and 120 ms.SC group showed reduced PPI compared to HC. PPI deficit was the most prominent at 60 ms LI, and was right-sided only at 120-ms LI. DSB group demonstrated left-sided reduced PPI at 60 ms LI and left eye ASR latency reduction at 120 ms LI. SC exhibited the highest (0,87), and HC the lowest (0,39) S2/S1 ratio in P50 paradigm; the intermediate value (0,67) was found in DSB patients. In both patient groups S2/S1 ratio significantly (p < 0,001) differed from that in HC. No significant differences were revealed in P50 and PPI measures between patient groups that may be related to high variability in SC group.Left-side PPI deficit in DSB patients is possibly related to right hemisphere disturbances that are inherent to patients with sexual disorders. P50 and PPI measures may be useful to identify schizophrenic disorder in patients with DSB.

The Neural Substrates of Visual Perceptual Learning of Words: Implications for the Visual Word Form Area Hypothesis

It remains under debate whether the fusiform visual word form area (VWFA) is specific to visual word form and whether visual expertise increases its sensitivity (Xue et al., 2006; Cohen et al., 2002). The present study examined three related issues: (1) whether the VWFA is also involved in processing foreign writing that significantly differs from the native one, (2) the effect of visual word form training on VWFA activation after controlling the task difficulty, and (3) the transfer of visual word form learning. Eleven native English speakers were trained, during five sessions, to judge whether two subsequently flashed (100-msec duration with 200-msec interval) foreign characters (i.e., Korean Hangul) were identical or not. Visual noise was added to the stimuli to manipulate task difficulty. In functional magnetic resonance imaging scans before and after training, subjects performed the task once with the same noise level (i.e., parameter-matched scan) and once with noise level changed to match performance from pretraining to posttraining (i.e., performance-matched scan). Results indicated that training increased the accuracy in parameter-matched condition but remained constant in performance-matched condition (because of increasing task difficulty). Pretraining scans revealed stronger activation for English words than for Korean characters in the left inferior temporal gyrus and the left inferior frontal cortex, but not in the VWFA. Visual word form training significantly decreased the activation in the bilateral middle and left posterior fusiform when either parameters or performance were matched and for both trained and new items. These results confirm our conjecture that the VWFA is not dedicated to words, and visual expertise acquired with training reduces rather than increases its activity.

Dichotic words listening test: technical aspects and results in normal right-handed individuals

Dichotic listening tests have been being used in an increasing frequency to determine in a non-invasive way the cerebral dominance in right- and left-handed patients. This is especially relevant when surgery in eloquent brain areas is being contemplated. A Portuguese version of the dichotic words listening test was developed based mainly on Wexler's protocol. It consisted of 15 pairs of words with a stimulus dominance lower than 50%. They were recorded using natural voice and time and intensity synchronization by means of a specialized software. Each pair of words was presented twice in different channels within each block. The items were randomized and presented with a 300 msec interval between each trial. Four blocks of 30 pairs of words each were created, totalizing 120 trials. In the scoring process, the words heard over the right and left ears were wrote down. The number of times each word was heard over each ear was computed and their values subtracted yielding a partial score for each specific word pair. This process was repeated for all stimuli pair and a final score for right and left predominance was then reached. Thirty-two right handed normal individuals underwent the test 93.8% showed a right ear advantage. These results are very similar to the actual left hemisphere dominance rate in a right-handed population.

Disabled vs Nondisabled Readers: Perceptual vs Higher-Order Processing of One vs Three Letters

12 disabled and 12 nondisabled readers (mean age, 11 yr.) were compared on a letter-search task which separated perceptual processing from higher-order processing. Participants were presented a first stimulus (for 200 msec. to minimize eye movements) followed by a second stimulus immediately to estimate the amount of information initially perceived or after a 3000-msec. interval to examine information more permanently stored. Participants were required to decide whether any letter present in the first stimulus was also present in the second. Two processing loads (1 and 3 letters) were examined. Disabled readers showed more pronounced deficits when they were given very little time to process information or more information to process.

Neural limitations of visual excitability. VII. Nonhomonymous retrochiasmal interaction

Visual excitability changes were obtained from two trained observers by measuring threshold with a brief test flash of light at varying temporal intervals from the onset of a longer, supraliminal conditioning flash. The test target was either a 1°20' or a 5°20' solid disc, and was exposed to the right eye at 6°40' along the horizontal meridian in the temporal half field. The conditioning target was a 6°40' disc containing central masks of various angular subtenses, and was so placed in the left eye that the resulting annuli surrounded the test target in the binocularly fused field of view. For all conditions, threshold rose when test preceded conditioning flash in time, reaching a maximum at about o-msec interval between onsets. As the test flash was progressively delayed in time, thresholds fell to an asymptote, returning to resting level after termination of the conditioning flash. The smaller the mask diameter in the center of the conditioning target, i.e., the tighter the fit around the binocularly fused test target, the greater the maximum rise in threshold in the other eye. With small test targets, greater threshold changes were produced by conditioning targets with small masks than by those without a mask (solid targets). Observations on a third observer indicate that similar findings obtain when conditioning stimuli are equated for total luminous flux. These data indicate that retrochiasmal interaction is greater at target borders, and are compatible with recent unit studies on the cortical receptor field.

The Effect of Temperature on Locust Flight Muscle

Mechanical and electrical responses were studied in isolated nerve-muscle preparations at various temperatures, mainly in relation to current problems in locust flight. 1. The delay between the peak of the action potential and the onset of a twitch is 1 msec. and independent of temperature from 30 to 45° C. (the range encountered in sustained flight), indicating that physical rather than chemical processes are responsible for the main time-consuming links in the excitation-contraction coupling. 2. There is no mechanical staircase effect in a succession of twitches and no post-tetanic potentiation so that identical and closely spaced twitches, as well as doubly fired contractions, can follow each other in long trains. 3. Above 25° C., the tetanus: twitch ratio is 2 and the work is independent of temperature. 4. Two closely timed stimuli (double firing; 2-10 msec. interval) may result in 2 to 3 times more work than in a twitch. The increase is graded by the interval and the contraction is prolonged over that of the twitch only by this interval. 5. The twitch durations are smaller than previously reported so that the loss of energy due to interaction between antagonists is insignificant during normal flight, in both singly and doubly fired contractions. 6. The temperature-dependence of locust flight is in accordance with the properties of the isolated nerve-muscle preparation.

Neural limitations of visual excitability. IV: spatial determinants of retrochiasmal interaction

Visual excitability changes were obtained from two trained observers by measuring threshold with a test flash of light at varying temporal intervals from a supraliminal conditioning flash. In monocular observation the two flashes were presented to the same eye; in binocular observation the conditioning flash was exposed to one eye and the test to the homonymous location in the other eye. The conditioning target size was varied while the concentrically placed test flash was held constant. In all instances, threshold rose when test preceded conditioning flash in time, reaching a maximum at about a o-msec interval. As test flash was progressively delayed with respect to conditioning flash onset, thresholds fell to an asymptote, returning to resting level only after termination of the conditioning flash. Both monocularly and binocularly, an increase in the magnitude of threshold rise was produced by making the conditioning target smaller, the greatest proportionate effect being obtained binocularly. These findings indicate that central (retrochiasmal) processes are critical with respect to spatial interaction in the visual system, a conclusion compatible with recent studies on the cortical receptor field.