Motor inhibition of return can affect prepared reaching movements.

Inhibition of return (IOR) is a widely studied phenomenon that is thought to affect attention, eye movements, or reaching movements, in order to promote orienting responses toward novel stimuli. Previous research in our laboratory demonstrated that the motor form of saccadic IOR can arise from late-stage response execution processes. In the present study, we were interested in whether the same is true of reaching responses. If IOR can emerge from processes operating at or around the time of response execution, then IOR should be observed even when participants have fully prepared their responses in advance of the movement initiation signal. Similar to the saccadic system, our results reveal that IOR can be implemented as a late-stage execution bias in the reaching control system.

Saccadic inhibition of return can arise from late-stage execution processes.

Inhibition of return (IOR) is thought to improve the efficiency of visual search behaviour by biasing attention, eye movements, or both, toward novel stimuli. Previous research suggests that IOR might arise from early sensory, attentional or motor programming processes. In the present study, we were interested in determining if IOR could instead arise from processes operating at or during response execution, independent from effects on earlier processes. Participants made consecutive saccades (from a common starting location) to central arrowhead stimuli. We removed the possible contribution of early sensory/attentional and motor preparation effects in IOR by allowing participants to fully prepare their responses in advance of an execution signal. When responses were prepared in advance, we continued to observe IOR. Our data therefore provide clear evidence that saccadic IOR can result from an execution bias that might arise from inhibitory effects on motor output neurons, or alternatively from late attentional engagement processes.

Evaluation of reading comprehension with neuropsychological and event-related brain potential (ERP) methods.

Evidence is presented for the efficacy of a new method of assessing reading comprehension using a standardized reading test that was formatted for computer presentation with simultaneous event-related brain potential (ERP) recordings. Reading comprehension abilities of 23 healthy undergraduate students were evaluated using ERPs. The results revealed a differential ERP response pattern for correct and incorrect test items. These response patterns were observed at individual participant levels. The findings provided further support for the use of ERPs in the neuropsychological assessment of patients who are difficult or impossible to assess using behavioral responses because of concomitant motoric and/or communicative limitations.

Fatigue after stroke.

OBJECTIVE: To determine the frequency and outcome of fatigue, its impact on functioning, and its relationship with depression in patients 3 to 13 months poststroke. DESIGN: Survey. SETTING: Community. PARTICIPANTS: Eighty-eight individuals from a pool of 181 consecutive patients previously admitted to an acute stroke service who were willing and able to complete the self-report questionnaires, and 56 elderly controls living independently in the community. MAIN OUTCOME MEASURES: Fatigue Impact Scale (a self-report measure of the presence and severity of fatigue and its impact on cognitive, physical, and psychosocial functions) and the Geriatric Depression Scale. RESULTS: The frequency of self-reported fatigue problems was greater in the stroke group (68%) than in the control group (36%, p < .001) and was not related to time poststroke, stroke severity, or lesion location. Forty percent of the stroke group reported that fatigue was either their worst or one of their worst symptoms. Patients attributed more functional limitations to their fatigue than did control subjects with fatigue. Although the presence of fatigue was independent of depression, the impact of fatigue on functional abilities was strongly influenced by depression. CONCLUSION: Fatigue can contribute to functional impairment up to 13 months after stroke, and its recognition and treatment are important for maximizing recovery.

Turning body time to shift time.

Studies have shown that shift work can have a negative impact on job performance, sleep, physical and emotional health, social life, family life, drug use and level of job-related stress. For nurses, these negative effects have consequences not just for the individual, but for the workplace, as decreased alertness and reduced job performance could endanger human lives.

Effects of light therapy on neuropsychological function and mood in seasonal affective disorder.

To date, little attention has been paid to changes in neuropsychological function in seasonal affective disorders (SAD). In this study, we investigated the performance of 30 patients with SAD on a wide range of cognitive variables before and after 2 weeks of light treatment with either white or placebo red light, as well as later in the summertime. Performance of subjects with SAD on neuropsychological tests was compared with a group of 29 age- and education-matched healthy control subjects. The most consistent deficits associated with SAD were on tests of cognitive failures, visual memory, and visual-construction skills. In contrast to specific bright light effects on psychiatric measures, reports of cognitive failures did not change with either light treatment. Visual memory and constructional deficits responded nonspecifically to treatment with either white or the presumed placebo red light. Surprisingly, visual memory deficits were seen again in the summer, at a time when mood, cognitive failures, and other cognitive functions appeared at normal levels. These data suggest that cognitive functioning is affected by SAD. In addition, light treatment may have differential effects on mood and cognition.

Lesions dorsal to the suprachiasmatic nuclei abolish split activity rhythms of hamsters.

Constant light exposure (LL) can result in "splitting" of circadian rhythms into two components coupled about 12 hr apart. Splitting has been interpreted as evidence for the presence of two main oscillators or groups of oscillators underlying circadian rhythms. Abolition of splitting after unilateral suprachiasmatic nucleus ablation suggested that each suprachiasmatic nucleus could correspond to one of these component oscillators. We examined whether lesions outside the suprachiasmatic nuclei (SCN) would abolish split activity rhythms of hamsters in LL. Wheel-running activity was recorded for 3 months after surgery. Tissue damage was assessed by Klüver-Barrera staining. Damage to areas dorso-caudal to the SCN was able to abolish the split condition. Bilateral damage to the anterior SCN, partial unilateral SCN ablation or unilateral periventricular damage also abolished the split pattern. These results indicate that destruction of one SCN is not essential for the elimination of split rhythms since lesions dorsal to the SCN or partial bilateral SCN damage are also effective. Indirect lesion effects on SCN function or damage to extra-SCN oscillators may account for the loss of the split condition.

Comprehension of concrete and abstract words in autistic children.

This study employed the Stroop paradigm to examine comprehension of single words in autistic children. The words of interest varied along a concrete-abstract dimension. In the Stroop paradigm, subjects are asked to name the color of ink in which color words are printed. Comprehension is indexed by the degree to which the automatic processing of words interferes with the color-naming task. For both concrete and abstract words, autistic children showed the same degree of interference as reading-matched controls. The findings corroborate and extend previous work suggesting that autistic children understand, and by implication, can mentally represent, at least some word meanings.

Horizontal knife cuts in the suprachiasmatic area prevent hamster gonadal responses to photoperiod.

We used horizontal knife cuts near the suprachiasmatic nucleus (SCN) to investigate the route for day-length information transmission from the SCN to the paraventricular nucleus (PVN). Testicular regression was blocked in animals with knife cuts dorsal to the SCN that spanned its entire rostrocaudal extent, and in PVN-ablated animals. Misplaced cuts in the ventral preoptic area also prevented gonadal regression. These neural insults did not systematically affect the circadian control of activity rhythms. The pathway from the SCN to the pineal runs from the dorsal border of the SCN and travels through the periventricular area toward the PVN.

Short-day exposure eliminates the LH response to naloxone in golden hamsters.

Short-day-induced testicular regression in golden hamsters is accompanied by changes in opiatergic control of LH release. Serum LH in long-day-exposed hamsters is elevated by subcutaneous injections of naloxone. By day 42 of short-day exposure, naloxone is unable to stimulate LH secretion; responsiveness to naloxone is restored after reexposure to long days. The change in response to naloxone may reflect a loss of opiate regulation of LH release; an alternative, but not mutually exclusive, hypothesis is that additional opiate-independent mechanisms inhibit LH despite the blockade of opiate LH inhibition by naloxone.

Periventricular and suprachiasmatic lesion effects on photoperiodic responses of the hamster hypophyseal-gonadal axis.

We examined the involvement of neural mechanisms within the suprachiasmatic nucleus (SCN) and periventricular area (PVA), and the role of prolactin (Prl) in control of endocrine function in short day-exposed Syrian hamsters. Hamsters bearing lesions of the SCN or PVA, hamsters implanted with an anterior pituitary under the kidney capsule to provide sustained Prl levels, and sham-operated hamsters were exposed to either 14L:10D or 8L:16D. After 9 wk, hamsters were sacrificed, and their testes and pituitaries were studied in vitro to assess their secretory capacity. SCN lesions and large periventricular lesions impinging on the paraventricular nucleus prevented testicular regression during short-day exposure. Small periventricular lesions and pituitary implants did not prevent gonadal regression in hamsters exposed to short days. Testis weights were positively correlated with basal and luteinizing hormone (LH)-stimulated androgen production in the control and lesioned groups; pituitary implants prevented the decline in androgen production in vitro in gonadally regressed animals. The relative in vitro pituitary response to gonadotropin-releasing hormone (GnRH) stimulation in control and lesioned groups was not reduced by short-day exposure. These data indicate that either axons coursing dorsally from the SCN or extra-SCN structures in the periventricular/paraventricular area are necessary for testicular regression in short photoperiods.

Neural control of the daily rhythm of sexual behavior in the male golden hamster.

Circadian and neural mechanisms important for the organization of reproductive behavior in the male golden hamster were examined. The sexual behavior of male hamsters exhibits diel variations; males are quicker to initiate copulation and to ejaculate in the dark phase than in the light phase of a daily light-dark cycle. The copulatory rhythm is endogenously generated and persists under constant environmental conditions. Destruction of the suprachiasmatic nuclei (SCN) eliminated the normal diurnal rhythm of sexual behavior without affecting copulation per se. In contrast to SCN lesion effects, damage to the medial preoptic area (MPOA) reduced or eliminated copulation; in those MPOA-ablated animals that continued to copulate, the circadian modulation of sexual behavior remained intact.

Gonadal responses to food restriction in intact and pinealectomized male golden hamsters.

Male golden hamsters underfed for 11-16 weeks showed a 30% decrease in body weight accompanied by significant testicular regression. Pinealectomy did not prevent underfeeding-induced gonadal regression. Resumption of ad-libitum feeding restored body weights to near control levels and permitted testicular redevelopment in animals with previously regressed tests. These data indicate that chronic food restriction can affect the reproductive status of hamsters and that this effect does not depend on an intact pineal gland. Body weight changes may serve as a secondary proximate cue in addition to photoperiod for timing the hamster seasonal breeding cycle.

Photoperiodic regulation of the hamster testis: dependence on circadian rhythms.

The testes of hamsters exposed to short days (10 hr of light per day) regress within 13 weeks. Administration of 7.5% deuterium oxide to hamsters lengthens the period of free running circadian activity rhythms by 2.2% and prevents testicular regression during short-day exposure. This consistent with predictions derived from an external coincidence model for photoperiodic time measurement: Deuterium oxide changes phase relationships between the light-dark cycle and the circadian system, the hamster's daily photosensitive phase is stimulated with light during short days, and the testes remain large. Conservation of the period of circadian rhythms within narrow limits has adaptive significance for hamster photoperiodism and for the occurrence and phasing of the annual reproductive cycle.