Hemispheric differences in tactuo-spatial processing

A tactual recognition task employing six random forms presented in each of eight 45° relative disorientations was given to ten normal blindfolded subjects. A consistent right hemisphere advantage was obtained. Pattern of scores, however, was similar for both hemispheres, suggesting that: (a) the right hemisphere is doing the processing; (b) the left hemisphere has access to the results of this; (c) the right hemisphere has access to the information gathered by the left hemisphere. The results suggest that information loss occurs during hemispheric transfer.     

Long-term cognitive outcome of hemiconvulsion-hemiplegia-epilepsy syndrome affecting the left cerebral hemisphere

Long-term cognitive outcome following hemiconvulsion–hemiplegia–epilepsy (HHE) syndrome has been poorly studied, with little attention to the implications of side of involvement in HHE. This retrospective study describes language lateralization and cognitive performance in five patients with HHE syndrome affecting the left cerebral hemisphere. All of the patients had to have intracarotid sodium amytal testing (IAT) to be included in this study. The mean age of the patients was 30.2 years (range: 13–50). All patients had their hemiconvulsive seizures before age 1½ years (range: 6–13 months). All patients had right-sided hemiatrophy of the body, left mesial temporal sclerosis, and seizures originating from the left temporal lobe. The habitual seizures began at a mean age of 4.5 years (range: 1.5–12 years). Performance on tests of intelligence, verbal memory, and visual memory was examined. Language was represented in the right cerebral hemisphere in three patients, the left hemisphere in one patient, and both hemispheres with predominance on the right side in the fifth patient. Intellectual functioning was in the borderline to extremely low range among the patients with right hemispheric or bilateral representation for language. These patients were variably impaired on measures of verbal and visual memory. The patient with left hemispheric representation for language performed in the average range on tests of intellectual functioning and verbal memory, whereas scores on visual memory were variable. This study demonstrated that reorganization of language to the right cerebral hemisphere or its bilateral representation is common in patients with HHE syndrome affecting the left cerebral hemisphere, and is associated with poor cognitive outcome.     

Novel effects on memory observed following unilateral intracranial administration of okadaic acid, cyclosporin A, FK506 and [MeVal4]CyA

The involvement of protein phosphatases and peptidyl-prolyl cis/trans isomerases (PPIases) in memory formation in the chick has previously been investigated using a single-trial learning task. In these studies, inhibitory agents were administered bilaterally directly to a critical area of the chick brain. These studies are now extended to investigate whether similar effects are obtained if the drugs are administered unilaterally. All of the effects reported previously following bilateral administration of okadaic acid (OA), cyclosporin A (CyA), FK506 and [MeVal⁴]CyA can be attributed to their action in just one hemisphere. OA, at a concentration known to selectively inhibit PP2A in vitro (0.5 nM) results in permanent memory loss from 30–40 min post-training when injected in the left hemisphere, but has no effect when injected in the right hemisphere. A higher concentration of OA (100 nM), which inhibits both PP2A and PP1 in vitro, has a similar effect in the left hemisphere but causes a transient period of memory loss from 10–20 min post-training when injected in the right hemisphere. CyA (5 nM and 20 nM), which inhibits both PP2B and PPIase activity, causes permanent memory loss from 60 min post-training when injected into the left hemisphere, an effect also observed following administration of FK506 (20 nM), which also inhibits PP2B and PPIase activity, and [MeVal⁴]CyA (5 nM), which inhibits PPIase activity but not PP2B activity. Administration of CyA (20 nM) and FK506, but not [MeVal⁴]CyA, in the right hemisphere leads to a transient period of memory loss from 10–20 min post-training. These results confirm significant roles for phosphatases and PPIases in memory processing but challenge previous conclusions drawn on the basis of bilateral drug administration protocols.     

Unilateral auditory language comprehension on the token test following cerebral commissurotomy and hemispherectomy

Two versions of the Token Test for auditory language comprehension were administered unilaterally to selected commissurotomy and post-infantile hemispherectomy patients. No deficit was found for the left hemisphere while the right showed a severe deficit comparable to that of left brain-damaged asphasics. Error analysis, however, revealed that the right hemisphere was more sensitive to perceptual and (short term auditory verbal) memory constraints in the task, whereas aphasics were more sensitive to linguistic variables. Mean overall scores of the right hemispheres on the Token Test were comparable to 4 yr old children as contrasted with a high mental age estimate—mean 11 yr— on the Peabody Picture Vocabulary Test. It is suggested that in the normally developing brain, distinct language functions exhibit disparate ontogeneses of lateralization in the left hemisphere.     

Visuospatial and other "right-hemispheric" functions after long recovery periods in left-hemispherectomized subjects

Two subjects who had infantile brain damage and left hemispherectomies at the ages of 17 and 18 yr are assessed after 28 and 16 yr recovery periods. Both have intact language and verbal memory abilities. However, on functions normally mediated predominantly by the right hemisphere, including nonverbal memory, higher cognitive visuospatial skills, and complex extrapersonal orientation ability, they are severely impaired. Simple visuospatial perceptual and orientation abilities, emotional expression, and face recognition, also "right-hemispheric" functions, are normal. It is postulated that the right hemisphere, if isolated in infancy, has the potential to take over most cognitive functions. The pattern of intact and impaired abilities shown by these subjects allows a hierarchy of functionally important abilities to be constructed. The functions mediated by the solitary right hemisphere are those most essential for independent survival, and functions that are not represented are those least required.     

Hemispheric asymmetries in memory processes as measured in a false recognition paradigm

Although memory differs in important ways between the left and right cerebral hemispheres, the nature of these differences remains controversial. We examined this issue in two experiments using a false memory paradigm that allowed novel tests of two theories that have not been assessed in a common paradigm previously. Lists of semantically related words (e.g., bed, rest, wake…), all highly associated to one “critical” word (e.g., sleep), were presented auditorily during a study phase. Memory for both the related words and the critical words was measured in a subsequent old/new recognition test using divided-visual- field word presentations. The most important results were that the ability to correctly reject previously unpresented words was greater when test items were presented to the right visual field/left hemisphere (RVF/LH) than to the left visual field/right hemisphere (LVF/RH) and that participants were more confident in correctly rejecting unpresented words when test items were presented to the RVF/LH than to the LVF/RH. Results were in line with the theory that associative activation of semantic information is restricted in the left hemisphere but diffuse in the right; however, these results contrasted with the theory that memory traces are interpretive in the left hemisphere but veridical in the right. A potential resolution to the seemingly contradictory theories of asymmetries in memory processing is briefly discussed.     

Tone probe event-related potential differences during a face recognition task in prepubertal children and Turner Syndrome girls

Hormones have been shown to play a role in both cerebral development and neurocognitive function. Turner Syndrome (TS) provides the opportunity to study the effect of the lack of estrogen on neurocognitive development. In this study, event-related potential (ERP) differences were examined among 12 TS girls, 20 prepubertal control girls, and 20 prepubertal control boys during a face recognition memory task. Stage of puberty was determined by Tanner Scale rating and hormonal assay. ERPs to pairs of auditory probe stimuli were recorded from eight scalp sites while participants performed a faced recognition memory (FRM) task. For the N2 component of the ERP (which has previously been associated with evaluation of stimulus information, categorization difficulty, and attention), control boys displayed greater right versus left hemisphere amplitude, control girls displayed greater left versus right hemisphere amplitude, and there was no amplitude asymmetry for TS girls. Further, control girls had greater left hemisphere N2 amplitude than control boys and TS girls, and greater right hemisphere N2 amplitude than TS girls. The results suggest more right hemisphere activation during face recognition in boys, while the opposite pattern was present in control girls. In contrast, TS girls displayed no asymmetry, indicative of more uniform involvement of the left and right hemispheres during face recognition. These findings are consistent with differences in cortical organization related to face recognition memory processing among prepubertal control boys, girls, and TS girls. They also support the notion that sex differences in cognitive function are present prior to pubertal onset, and that lack of endogenous sex hormones (e.g., estrogen) during prenatal/perinatal development (i.e., for TS girls) may influence brain organization and, in turn, neurocognitive processes that relate to face recognition.     

Differential right hemispheric memory storage of emotional and non-emotional faces

Seventy-two female subjects memorized two photographed faces and subsequently discriminated these “target” faces from two “non-target” faces. The faces were presented unilaterally for 150 msec, and manual reaction times for the discriminations served as the dependent variable. The face stimuli were either “neutral” or “emotional” in facial expression, these attributes having been shown, by a preliminary study, to be highly reliable. Faster reaction times were obtained for left visual field than for right visual presentation. Subjects (N = 36) who memorized emotional faces showed significantly faster discrimination of faces presented in the left than in the right visual field (25·7 msec); subjects (N = 36) who memorized faces lacking emotional expression also showed significant left visual field superiority (11·6 msec), but this left field superiority was significantly smaller than that of subjects memorizing emotional faces. Results are consistent with previous tachistoscopic evidence of right hemisphere superiority in face recognition speed and with diverse non-tachistoscopic evidence of preferential memory storage of affective material. The pattern of latencies for the different visual field-response hand conditions supported a model of lateral specialization in which the specialized hemisphere normally processes both directly-received and interhemispherically- transferred stimuli.     

Intracarotid amobarbital procedure and prediction of postoperative memory in patients with left temporal lobe epilepsy and hippocampal sclerosis

PURPOSE: Although temporal lobe epilepsy (TLE) patients with dominant hemisphere hippocampal sclerosis generally have good cognitive outcome after anterior temporal lobectomy (ATL), a minority of patients experience at least mild post-ATL decline on one or more standardized measures of episodic and semantic memory. The goal of this investigation was to determine whether memory outcome in this group could be predicted from preoperative intracarotid amobarbital procedure (IAP) recognition memory scores. METHODS: Data from 22 left TLE patients were studied retrospectively. All were left hemisphere language dominant and had IAP scores for each hemisphere, a significant degree of pathology-confirmed left hippocampal sclerosis (HS+), and no positive MRI findings other than atrophy. Cognitive outcome status was represented by the number of pre- to post-ATL declines across three tests, as defined by 90th percentile Reliable Change Index (RCI) criteria. RESULTS: Only 14% of the sample exhibited decline on more than one memory test. Low right IAP (left hemisphere injection) scores and relatively high preoperative cognitive ability and age at surgery predicted a greater risk of post-ATL memory decline. CONCLUSIONS: A minority of left TLE HS+ patients experience at least a mild degree of RCI-defined decline in episodic or semantic memory after ATL. The right hemisphere IAP memory score, which reflects the functional reserve of the contralateral hemisphere, can help predict the risk of postoperative memory decline for TLE patients in whom HS+ is likely based on the presence of hippocampal atrophy on MRI or early age of seizure onset.     

Hemispheric efficiency in middle and later adulthood.

Right and left hemisphere efficiency, as measured by dichotic memory for numbers, was assessed in a sample of older adults in Experiment I. Right hemisphere efficiency dropped off sharply with age, while left hemisphere efficiency did not show a significant decline. A second group of subjects was tested on a musical note recognition task in Experiment II. Regression analyses revealed significant age decrements in performance, regardless of ear/hemisphere involved. The writers suggested that the reported decline with age in spatial ability may result from an age related decline in right hemispheric functioning, even on tasks that are right hemisphere dominant. The lack of decline reported for verbal ability may be a consequence of the lack of decline in left hemisphere efficiency with regard to left hemisphere dominant tasks.     

Functional dissociation of the hemispheres using foveal visual input

A consistent 10 (± 2.2) msec visual field superiority in vocal RT to letters was found using both foveal and extra-foveal input (0.5°, 2° and 4° eccentricities), when typical procedures in the paradigm were modified. This consistency occurred in both the right visual field (for extreme right-handers) and left visual field (for extreme left-handers). A second experiment using a recognition memory task with manual RT also revealed concurrent opposite hemisphere superiorities for letters and geometric forms presented only 5.2–20.7' left or right of fixation. Acuity differences, directional scanning, and asymmetric cerebal activation could not account for the results. A substantial splitting of cortical connections from the innermost fovea is thereby indicated, as well as the viability of using foveal-only input in studies of cerebral functional asymmetries.     

Hemisphere memory of concrete and abstract information determined with the intracarotid Sodium Amytal test

An extended version of the bilateral intracarotid Sodium Amytal test was administered pre-operatively to 13 patients with intractable complex partial epileptic seizures, to determine cerebral hemisphere speech and memory. There were 6 patients with left temporal lobe lesions and 7 patients with right temporal lobe lesions. Amobarbital (175 mg, 10%), injected on 2 occasions, determined the left hemisphere to be speech dominant in all cases. Memory assessed with recall, cued recall, and recognition of concrete/abstract words and pictures, was studied on 3 occasions: in a baseline test considered to indicate the degree of patient cooperation and the bilateral hemisphere memory; in a right hemisphere Amytal test; and in a left hemisphere Amytal test. The specific data pattern obtained, that abstract pictorial information is most efficiently processed by an intact right hemisphere and that verbal information is processed best by an intact left hemisphere, demonstrates the reliability of the approach taken here to present abstract and concrete to be remembered information.     

Laterality and Types of Dyslexia

ANNETT, M. Laterality and types of dyslexia. NEUROSCI BIOBEHAV REV 20(4) 631–636, 1996.—The right shift theory of handedness and cerebral specialization suggests that there is an underlying substrate of random lateral asymmetries in all higher animals and a specific factor in humans which increases the probability of left hemisphere advantage. The specific factor displaces the random distribution along a continuum of asymmetry in favour of the left hemisphere and the right hand. The distribution of handedness in families can be explained if the shift to dextrality depends on a single gene, rs +, when the frequency of the gene is estimated from the proportion of dysphasics with unilateral lesions of the left versus the right hemisphere. The genotype proportions suggested a genetic balanced polymorphism with heterozygote advantage for laterality and ability.

Application of the model to developmental dyslexia led to the hypothesis that both homozygotes (rs −− and rs ++ genotypes) are at risk for reading. The critical question was whether the type of cognitive problem differs as expected, speech based processing for the rs −− and non-speech based for the rs ++. The former should include more left and mixed handers, while the latter should be more strongly dextral than controls. Evidence for this double dissociation between type of cognitive disability and type of handedness has been found in poor readers and in other samples. Copyright © 1996 Elsevier Science Ltd.     

Tactual Recognition of Cognitive Stimuli : Roles of Hemisphere and Lobe

Four groups of focal brain-damaged patients, involving left and right hemisphere damage with or without the involvement of parietal lobe, and a control group of general medical patients, were required (a) dichaptically to perceive two cognitive stimuli (letter-letter, figure-figure, or letter-figure), and (b) haptically match the target stimulus from a set of test stimuli. The number of trials taken to match the target stimulus correctly was the dependent measure. The significant main effect of lobe suggested that the parietal lobe is the primary locus for tactual recognition. All interaction effects involving lobe were nonsignificant. The main effect of hemisphere was nonsignificant, although the interaction of hemisphere x lobe was significant. Left and right hemisphere damaged patients required more trials to recognize "letter" and "figure", respectively.     

Tactual recognition of cognitive stimuli: roles of hemisphere and lobe.

Four groups of focal brain-damaged patients, involving left and right hemisphere damage with or without the involvement of parietal lobe, and a control group of general medical patients, were required (a) dichaptically to perceive two cognitive stimuli (letter letter, figure figure, or letter figure), and (b) haptically match the target stimulus from a set of test stimuli. The number of trials taken to match the target stimulus correctly was the dependent measure. The significant main effect of lobe suggested that the parietal lobe is the primary locus for tactual recognition. All interaction effects involving lobe were nonsignificant. The main effect of hemisphere was nonsignificant, although the interaction of hemisphere x lobe was significant. Left and right hemisphere damaged patients required more trials to recognize "letter" and "figure", respectively.     

Memory in functional psychosis.

Acute schizophrenic, chronic schizophrenic, and depressive patients (20 of each) were compared with normal subjects and six groups of patients with organic brain disease. They were given tests of verbal learning (left hemisphere type function) and pattern recognition memory (right hemisphere type function). All functional psychotics showed impaired memory. Acute schizophrenics were, however, only impaired on the verbal task, suggesting left hemisphere dysfunction, while chronic schizophrenics and depressives were impaired on both tasks, suggesting bilateral dysfunction.     

Lateralized cognitive dysfunction and psychotic symptoms in schizophrenia

Our understanding of hemispheric asymmetries in schizophrenia can be attributed to extensive neuropsychological and neuroimaging research on this topic; however, it has yet to be determined whether lateralized cognitive dysfunction represents a single core trait in schizophrenia or whether the lateralized impairments are domain specific. To test whether lateralized deficits are core features in schizophrenia we examined performance across a wide range of lateralized cognitive domains including attention, fluency, recognition memory, perception, and arousal. We also examined the relationship between lateralized impairments and psychotic and affective symptoms to determine whether abnormal hemispheric asymmetries were possibly state-related. The sample consisted of 43 subjects with schizophrenia and 66 normal healthy comparison subjects without psychiatric illness. Schizophrenia subjects exhibited abnormal right hemisphere performance on a test of recognition memory and abnormal left hemisphere performance on a measure of arousal. These findings suggest that lateralized cognitive disturbances in schizophrenia do not represent a single core lateralized deficit. Regarding the symptom analyses, severity of positive symptoms was related to right hemisphere cognitive impairment (including fluency and recognition memory), whereas severity of negative symptoms was related to left hemisphere cognitive impairment (including fluency). Overall, our findings suggest that lateralized dysfunction can occur in both hemispheres in schizophrenia, and that the positive psychotic symptoms may relate more to right hemisphere impairment, whereas negative psychotic symptoms may related more to left hemisphere impairment.     

Lateralization of Brain Mechanisms Underlying Automatic and Controlled Forms of Spatial Orienting of Attention

GAINOTTI, G. Lateralization of brain mechanisms underlying automatic and controlled forms of spatial orienting of attention. NEUROSCI BIOBEHAV REV 20(4)617–622, 1996.—Unilateral Spatial Neglect (USN) can be considered as a defect in spatial orienting of attention toward the half space contralateral to the damaged hemisphere. Since the classical work of Brain, W. R. Brain 64:224–272 (1941), several authors have emphasized that this defect is definitely more frequent and severe in patients with right brain damage, but the reason for this hemispheric asymmetry has remained controversial. Several investigations conducted with different experimental paradigms in different laboratories have shown that only automatic orienting of attention toward stimuli arising in the half space contralateral to the damaged hemisphere is disrupted in USN, whereas controlled, volitional orienting can be more or less completely spared. The hypothesis that at the level of the right hemisphere, spatial orienting of attention may be mainly prompted by automatic mechanisms may, therefore, be advanced. By contrast, the left hemisphere might play a leading role in mechanisms underlying volitional orienting of attention. According to this model, recovery from USN could be due to the substitution of the lost automatic orienting mechanisms with the spared volitional orienting mechanisms subserved by the intact left hemisphere. Copyright © 1996 Elsevier Science Ltd.     

Long-term cognitive outcome of hemiconvulsion–hemiplegia–epilepsy syndrome affecting the left cerebral hemisphere

Long-term cognitive outcome following hemiconvulsion–hemiplegia–epilepsy (HHE) syndrome has been poorly studied, with little attention to the implications of side of involvement in HHE. This retrospective study describes language lateralization and cognitive performance in five patients with HHE syndrome affecting the left cerebral hemisphere. All of the patients had to have intracarotid sodium amytal testing (IAT) to be included in this study. The mean age of the patients was 30.2 years (range: 13–50). All patients had their hemiconvulsive seizures before age 1½ years (range: 6–13 months). All patients had right-sided hemiatrophy of the body, left mesial temporal sclerosis, and seizures originating from the left temporal lobe. The habitual seizures began at a mean age of 4.5 years (range: 1.5–12 years). Performance on tests of intelligence, verbal memory, and visual memory was examined. Language was represented in the right cerebral hemisphere in three patients, the left hemisphere in one patient, and both hemispheres with predominance on the right side in the fifth patient. Intellectual functioning was in the borderline to extremely low range among the patients with right hemispheric or bilateral representation for language. These patients were variably impaired on measures of verbal and visual memory. The patient with left hemispheric representation for language performed in the average range on tests of intellectual functioning and verbal memory, whereas scores on visual memory were variable. This study demonstrated that reorganization of language to the right cerebral hemisphere or its bilateral representation is common in patients with HHE syndrome affecting the left cerebral hemisphere, and is associated with poor cognitive outcome.     

Hemispheric asymmetry in tactile forgetting induced by tactually-guided movement

Asymmetries in tactile short-term memory related to differential specialization of the cerebral hemispheres were studied in normal human adults using the Brown-Peterson distractor task. When the distractor was an auditory arithmetic task, no difference emerged between the two hands for the retention of touches to the fingers; however, when the distractor was a tactual maze task executed by the right hand, asymmetry in favor of the left hand was observed. Specifically, when the right hand performed the tactual maze, there was greater interference with tactile memory than when the left hand performed the maze, independent of which hand received the memory material. The results support a characterization of short-term memory as embracing multiple, limited storage capacities divided along the lines of processing demands, arising from different classes of material, placed on the two cerebral hemispheres.