Self-produced locomotion restores visual capacity after striate lesions

Perspectives on sensory processing disorder: a call for translational research

THIS ARTICLE EXPLORES THE CONVERGENCE OF TWO FIELDS, WHICH HAVE SIMILAR THEORETICAL ORIGINS: a clinical field originally known as sensory integration and a branch of neuroscience that conducts research in an area also called sensory integration. Clinically, the term was used to identify a pattern of dysfunction in children and adults, as well as a related theory, assessment, and treatment method for children who have atypical responses to ordinary sensory stimulation. Currently the term for the disorder is sensory processing disorder (SPD). In neuroscience, the term sensory integration refers to converging information in the brain from one or more sensory domains. A recent subspecialty in neuroscience labeled multisensory integration (MSI) refers to the neural process that occurs when sensory input from two or more different sensory modalities converge. Understanding the specific meanings of the term sensory integration intended by the clinical and neuroscience fields and the term MSI in neuroscience is critical. A translational research approach would improve exploration of crucial research questions in both the basic science and clinical science. Refinement of the conceptual model of the disorder and the related treatment approach would help prioritize which specific hypotheses should be studied in both the clinical and neuroscience fields. The issue is how we can facilitate a translational approach between researchers in the two fields. Multidisciplinary, collaborative studies would increase knowledge of brain function and could make a significant contribution to alleviating the impairments of individuals with SPD and their families.

The sometimes pernicious role of theory in science

The role of theory in science is discussed in the context of understanding brain function. Historically, theories of brain functions have oscillated between localization and anti-localization beliefs. In the last 50 years, the important discoveries of the ascending reticular activating system (ARAS), feature extracting neurons and synaptic growth led many to orthodoxy. Research became more and more focused upon the elements comprising the nervous system and their interconnections. The mainstream belief became that many brain functions including consciousness were localized, certain kinds of brain injuries produced irreversible functional deficits. Contrary scientific challenges were discouraged by the omnipresence of such theory. Examples of theoretical "Einstellungen" in the areas of ARAS, coma, treatment of brain injuries and consciousness are given, as well as signs that the pendulum is swinging back to an approach to the system as a whole rather than a focus on its parts.

Experience-dependent neuropsychological recovery and the treatment of chronic alcoholism

This paper reviews the relationship between cognitive status and treatment outcome in chronic alcoholics, the natural history of recovery, and the role of cognitively oriented remediation programs in facilitating recovery. Seven studies of experience-dependent recovery are described in which behavioral improvement was noted. Various recommendations for treatment over the course of recovery are made, guided by anticipated changes in capacity to process complex information over time.

Housing conditions modulate the effects of intracerebral grafts in rats with brain lesions

The aim of this study was to examine whether the behavioural effects of intracerebral grafts in rats with brain lesions can be modulated by postoperative housing conditions. Sixty-six young adult female rats were used. Twenty-two rats were sham-operated (S) and 44 rats sustained a complete aspirative lesion (L) of the fimbria-fornix and overlying tissue. The cavity was used in half the rats as the implantation site for solid fetal septal transplants (LT). Two days later, half the rats of each group were housed in an 'enriched' condition (S.EC, L.EC and LT.EC); the other half remained in standard condition (S.SC, L.SC and LT.SC). Two and 10 months later, the rats were tested in a Hebb-Williams maze. Two months after surgery, there was a highly significant lesion effect, no graft effect and no environmental effect except in S rats, S.EC rats making fewer initial errors than S.SC rats. Ten months after surgery, L rats still made more errors than S rats and S.EC rats made fewer initial errors than S.SC rats; however, the lesion-induced deficits were significantly attenuated in LT.EC rats, but not in LT.SC rats. These data show that both the enriched environment and the implant were unable alone to promote behavioural recovery but, applied together, they reduced the lesion-induced deficits. Dorsal hippocampus acetylcholinesterase (AChE)-staining intensity was reduced by the lesions, but this reduction was partially compensated for by the grafts; however, environmental conditions did not affect AChE-staining significantly. This latter observation suggests that the graft-derived partial cholinergic reinnervation of the hippocampus probably does not underly the behavioural improvement observed only in LT.EC rats.

The neuropathology of amnesia

Relations between brain damage and memory disturbance are outlined with emphasis on the so-called amnesic syndrome. Following a brief introduction into forms of memory and memory failures, the basic causes of brain damaage (with relevance to amnestic failures) are described. Thereafter, the two best-known forms of brain damage-amnesia relations are reviewed: the consequences of damage to medial temporal lobe structures and to diencephalic regions. For the cases with medial temporal lobe damage, evidence is reported in greater detail for H.M., who has been examined more than any other amnesic patient for more than 30 years now, as a considerable amount of literature has accumulated on his behavior in diverse situations. Other cases with more or less circumscribed damage to medial temporal lobe structures are reviewed so as to outline criteria for or against the hypothesis that there are regions within the medial temporal lobe whose damage might be critical for the amnesic syndrome. Two cases of diencephalic amnesia are summarized in particular (cases of Mair et al., 1979) as they have received extensive neuropsychological and neuropathological investigation. Other cases with, for example, Korsakoff's disease are reviewed, as well as cases with diencephalic, or combined mesencephalic-diencephalic damage without nutritional causes. A third group of patients with massive, but still selective amnesic disturbances are then described: cases of basal forebrain damage, followed by descriptions of Alzheimer's disease which has similarities in the underlying neuropathology. This leads over to cases with more generalized intellectual deteriorations (dementia), which may have developed on the basis of primarily cortical damage or damage principally to basal ganglia structures. After reviewing cases with mainly material-specific memory failures--usually as a consequence of restricted neocortical damage--a separate section follows on patients in whom retrograde amnesia is the prominent symptom. The contribution of animal models of human amnesia is critically reviewed and discrepancies are analyzed between human and animal memory disturbances. This section emphasizes the value of investigating inter-dependencies between brain structures by pointing out that relations between memory disturbances and brain damage may be more complicated than apparent from a simple structure-function assignment. This aspect is further followed up in the conclusions.

A comparison of lateral peristriate and striate neocortical ablations in the rat

The effects of striate, lateral peristriate and sham ablations upon the post-operative reacquisition of visual discriminations were studied in two experiments. The results of Experiment 1 indicated that lesions restricted to the lateral peristriate neocortex rendered the rat incapable of resolving an oblique stripe discrimination. Seven of the 9 rats with striate ablations were unable to form the discrimination. The histological findings indicated that the deficit following lateral peristriate injury was not due to interruption of the geniculostriate system. However, the behavioral impairment in destriate rats corresponded to the degree of unintentional injury in lateral peristriate neocortex, but not medial peristriate tissue. In Experiment 2, the effects of these lesions were studied upon the post-operative reacquisition of either a non-reversal or reversal of a preoperatively acquired brightness discrimination. Animals with striate damage demonstrated considerable savings on the non-reversed brightness discrimination, and they acquired the reversal at a rate equal to that seen in animals with sham ablations. Rats with peristriate ablations showed no savings on the non-reversed brightness habit, and they required more extensive training than both the striate and sham groups on the reversal. These findings suggest that the frequently reported loss of a preoperative brightness habit following large posterior neocortex ablations is due to damage in the lateral peristriate neocortex rather than damage of the geniculostriate system. These results, taken with other literature, suggest an important role of the lateral peristriate neocortex in visuospatial sensory function.

Sensory environments, brain damage, and drugs: a review of interactions and mediating mechanisms

The sensory environment appears to play a greater role than was previously appreciated in the etiology of, and recovery from, brain damage. This paper reviews the interaction between brain damage and complex and deprived environments, the nature of mechanisms which may mediate these effects, and the studies of stimulant drug effects on these processes. It is suggested that our traditional concepts of causation and mediating mechanisms have been overly simple and that we need to move to a more holistic multidimensional interactive perspective.

Effects of environmental complexity and deprivation on brain anatomy and histology: a review

During the last 20 years the anatomical plasticity of the brain in response to sensory stimulation has been clearly demonstrated. This paper reviews the effects of environments rich in sensory stimulation versus those which are stimulus poor. Effects have been noted at all levels from the gross anatomical to the electromicroscopic. As compared to their stimulus-deprived counterparts, animals reared in complex environments tend to display greater cerebral weight and length and cortical depth. The greatest effects occur in the occipital cortex where histological studies have revealed expanded neuron perikaryonal and nuclear size and dendritic branching, more dendritic spines, alterations in synaptic numbers and morphology, and greater numbers of neuroglia. Different cortical areas and layers respond to different degrees. Some responses have also been noted in the underlying hippocampus, particularly in the dentate gyrus. The emerging data present a picture of a dynamic, plastic brain adapting homeostatically to the demands of its environment.

Effects of rearing in different environments on subsequent environmental preference in rats

Environmental preference of male rats reared during 2 months after weaning either in a complex and changing environment (EC) or in empty laboratory cages (SC) was assessed in 4 different experiments. For 2 weeks after differential rearing, rats were placed in groups of 6 in testing cages which were divided into 2 compartments with communicating holes. One of these compartments was empty; the other contained 6 objects (complex compartment). Daily, 3 objects were moved from 1 compartment to the other and replaced by new ones. The preference for any of the compartments was chiefly assessed by the localization of feces (Experiments I and II) and directly by the localization of the animals through videorecording (Experiments III and IV). Both EC and SC rats showed a significant preference for the empty compartment during both light and dark portions of the daily cycle, but particularly during the light portion.Moreover, EC and SC animals differed from one another in that the SC rats showed a stronger preferences for the empty compartment than the EC rats, especially when active. General preference for the empty compartment seemed to diminish slowly, but EC and SC rats tended to remain distinct in habitat selection, at least during the period tested. This behavioral difference, tentatively interpreted in terms of neophobia, might constitute a possible mechanism for automaintenance of differential rearing effects.

Depth perception after infant and adult visual neocortical lesions in light- and dark-reared rats

In 2 experiments the behavior of light- and dark-reared infant- and adult-operated striate rats were compared at 20-160 days of age on a visual cliff apparatus in which the depth of the deep side could be varied. Differential depth thresholds revealed that depth discriminative ability did not develop normally following removal of the striate cortex in infancy. Further, infant-operates who were reared in darkness following their operations performed less well than their light-reared, infant-operated counterparts. The infant-operated animals, regardless of their postoperative rearing condition, performed significantly better than did adult-operated animals after comparable post-operative recovery periods and testing. The results are discussed in terms of further specification of the role played by age of operation and by the interaction between visual experience and age of operation.

Recovery of pattern discrimination ability in rats receiving serial or one-stage visual cortex lesions

Two groups of 10 hooded rats were trained on a pattern discrimination between horizontal and vertical striped stimuli which were equated for contour-length and total luminous flux, and in which consistent local luminous flux cues were eliminated. In one group of rats, visual cortex removals were performed in two stages with training between the operations. Nine out of the 10 rats were able to relearn the pattern discrimination (median of 344 trials) after the completed bilateral visual cortex lesions in one stage. In agreement with previous studies, none of these animals were able to relearn the discrimination after more than 10 times (550 trial limit) the trials required for original learning. However, several rats with total one-stage lesions could relearn the pattern discrimination if very extended periods of training were given.