Multitask analysis of cerebral hemisphere specialization in monozygotic twins discordant for handedness.

This study constitutes a multitask appraisal of cerebral hemisphere specialization with 13 monozygotic (MZ) twin pairs discordant for handedness. Tasks included dichotic listening, finger tapping with concurrent loads, two tachistoscopic visual half-field tests, and a free-vision face test. Overall, MZ twins showed similar performance asymmetries on most tasks. Different asymmetries, however, were observed on the finger tapping with anagram load and visual half-field with chair stimuli. In these instances, asymmetries for left- and right-handed MZ twins were more similar to patterns reported in the literature for left- and right-handed singletons, respectively, than for opposite-handed co-twins.

A comparison of forgetting in an implicit and explicit memory task.

Among possible criteria for distinguishing separate memory systems for implicit and explicit memory is that of substantial differences in either the form or rate of forgetting. Prior literature has claimed both differential forgetting and equivalent forgetting for implicit and explicit tasks. Existing experimental data for word-stem completion and explicit control tasks were reviewed and shown to be inconclusive. Our experiments measure forgetting in comparable implicit and explicit memory tasks of stem completion and stem cued recall. The form and the rate of forgetting are essentially the same for these implicit and explicit tasks. Levels of processing and task conditions differ only in the level of initial learning or availability. Thus, either the implicit and explicit task reflect traces in the same memory system or they reflect traces in different systems that have identical forgetting dynamics.

Lateralized dual task interference in left-handers: initial value differences do not affect the outcome.

The study was conducted to clarify factors involved in dual-task finger-tapping interference. Left-handers, as assessed by hand-writing preference and left-hand baseline tapping advantage, tapped both alone and while solving anagrams. Even though the left-hand baseline tapping advantage was experimentally removed on some (adjusted) trials, greater left- than right-hand tapping interference was observed during concurrent task performance. This result coupled with previous findings for right-handed subjects [Kee and Cherry, Neuropsychologia, Vol. 28, pp. 313-316, 1990] indicates that lateralized interference effects are not merely due to initial baseline tapping differences as proposed by Willis and Goodwin [Neuropsychologia, Vol. 25, pp. 719-724, 1987].

Ciprostene and indomethacin partially reverse the mechanisms of distal end necrosis in the rat random skin flap.

Survival of random skin flap distal end depends on hemodynamic, cellular, and coagulation mechanisms. This study was designed to evaluate whether administration of ciprostene, a stable prostaglandin I2 analogue, and indomethacin, a cyclooxygenase-hydroperoxydase enzyme inhibitor, would improve the survival rate of random skin flaps. Forty-five male rats were divided into nine groups and injected with sesame oil (control), ciprostene (20 micrograms/kg/day), and/or indomethacin (2 mg/kg/day). Injections were done before (pretreatment for 4 days), after (posttreatment for 6 days), and before/after (pre/posttreatment for 4 and 6 days, respectively) the elevation of random dorsal skin flaps. In the pretreatment and pre/posttreatment studies, the flap survival rate of all drug-injected groups was significantly higher than that of the control group (p less than 0.02). In addition administration of ciprostene alone yielded a trend of better flap survival rate, which, however, was not statistically significant (p less than 0.12). Of interest in the posttreatment study, only the simultaneous administration of ciprostene and indomethacin significantly increased skin flap viability compared with the other groups (p less than 0.02). Therefore, the results demonstrated that administration of ciprostene and indomethacin either alone or together partially reversed the pathophysiological mechanisms that cause necrosis of random skin flap distal end. These pharmacological changes significantly improved random skin flap survival rate.

The use of 5-aminoimidazole-4-carboxamide riboside (AICA riboside) to improve random skin flap viability in the rat model.

Several experimental studies have demonstrated that granulocytes have an important role in causing the necrosis of ischemic tissue by capillary plugging and superoxide radical formation. Adenosine is spontaneously released by ischemic cells and inhibits the granulocytic superoxide radical formation. 5-Aminoimidazole-4-carboxamide riboside, a naturally occurring by-product in purine biosynthesis, stimulates the release of ischemic cell adenosine and indirectly blocks the granulocyte-induced tissue necrosis. 5-Aminoimidazole-4-carboxamide riboside (10-500 mg/kg) was administered intraperitoneally in a blinded fashion once (single dose, 30 minutes before surgery) or twice (double dose, 30 minutes before and 5.5 hours after surgery) in groups of rats. The controls received intraperitoneal saline solution in the same fashion. Each rat underwent the elevation of a caudally based random skin flap. The flap viability was determined in a blinded fashion on the seventh post-operative day and statistically compared by Fisher's exact test. When 300 or 500 mg/kg of 5-aminoimidazole-4-carboxamide riboside was given as a single dose, the mean percentage of rat skin flap necrosis (19.4% +/- 3.1% and 19.6% +/- 4.2%, respectively) was lower but not significantly different from that of the control group of rats (29.3% +/- 2.7%) (p less than 0.08). Additionally, two doses of 500 mg/kg of 5-aminoimidazole-4-carboxamide riboside yielded a mean percentage of rat skin flap necrosis (12.24% +/- 4.58%) much lower (21.68% +/- 3.18%) than that of the control group of rats (p = 0.056). Our blinded fashion study demonstrated an almost statistically significant reduction of random skin flap distal necrosis after intraperitoneal injection of high doses of 5-aminoimidazole-4-carboxamide riboside.(ABSTRACT TRUNCATED AT 250 WORDS)

Restoration of paralyzed orbicularis oculi muscle function by controlled electrical current.

A canine model of facial nerve paralysis was studied to apply controlled electrical current to the peripherally denervated orbicularis oculi muscle, in the attempt to effectively restore the absent function of this denervated muscle. After unilateral facial nerve neurotmesis was performed in eight dogs, the denervated orbicularis oculi muscles of four dogs were electrically stimulated for 75 postoperative days (40 min/day). Denervated and normal orbicularis oculi muscles were electrophysiologically studied and compared with the Student t test. During the study period, minimum closure of denervated treated orbicularis oculi muscles was evoked with average stimulus strength (80-ms duration) of 1.61 +/- 0.22 log mA x ms, not significantly different from that of denervated nontreated or normal orbicularis oculi muscles. From days 10 through 30 only, maximum closure of denervated treated orbicularis oculi muscles was achieved with mean pulse strength (80-ms duration) of 2.37 +/- 0.09 log mA x ms, significantly lower (P less than .01) than that evoking the same type of contraction from denervated nontreated muscles (80-ms duration, mean 2.83 +/- 0.10 log mA x ms). In addition, denervated treated muscle pulse strength eliciting maximum contraction was not significantly different from that of normal orbicularis oculi muscles during the same period. This finding was not observed, however, from day 40 through the end of the study. This investigation demonstrates (1) the transient reversal of denervation changes of paralyzed orbicularis oculi muscle by daily electrical stimulation, and (2) the feasibility of restoring orbicularis oculi muscle function by controlled electrical current.