Cortical Visual Impairment in Childhood: 'Blindsight' and the Sprague Effect Revisited

The paper discusses and provides support for diverse processes of brain plasticity in visual function after damage in infancy and childhood in comparison with injury that occurs in the adult brain. We provide support and description of neuroplastic mechanisms in childhood that do not seemingly exist in the same way in the adult brain. Examples include the ability to foster the development of thalamocortical connectivities that can circumvent the lesion and reach their cortical destination in the occipital cortex as the developing brain is more efficient in building new connections. Supporting this claim is the fact that in those with central visual field defects we can note that the extrastriatal visual connectivities are greater when a lesion occurs earlier in life as opposed to in the neurologically mature adult. The result is a significantly more optimized system of visual and spatial exploration within the ‘blind’ field of view. The discussion is provided within the context of “blindsight” and the “Sprague Effect”.

The Inferior Colliculus in Alcoholism and Beyond

Post-mortem neuropathological and in vivo neuroimaging methods have demonstrated the vulnerability of the inferior colliculus to the sequelae of thiamine deficiency as occurs in Wernicke-Korsakoff Syndrome (WKS). A rich literature in animal models ranging from mice to monkeys-including our neuroimaging studies in rats-has shown involvement of the inferior colliculi in the neural response to thiamine depletion, frequently accomplished with pyrithiamine, an inhibitor of thiamine metabolism. In uncomplicated alcoholism (i.e., absent diagnosable neurological concomitants), the literature citing involvement of the inferior colliculus is scarce, has nearly all been accomplished in preclinical models, and is predominately discussed in the context of ethanol withdrawal. Our recent work using novel, voxel-based analysis of structural Magnetic Resonance Imaging (MRI) has demonstrated significant, persistent shrinkage of the inferior colliculus using acute and chronic ethanol exposure paradigms in two strains of rats. We speculate that these consistent findings should be considered from the perspective of the inferior colliculi having a relatively high CNS metabolic rate. As such, they are especially vulnerable to hypoxic injury and may be provide a common anatomical link among a variety of disparate insults. An argument will be made that the inferior colliculi have functions, possibly related to auditory gating, necessary for awareness of the external environment. Multimodal imaging including diffusion methods to provide more accurate in vivo visualization and quantification of the inferior colliculi may clarify the roles of brain stem nuclei such as the inferior colliculi in alcoholism and other neuropathologies marked by altered metabolism.

Superior Colliculus Lesions Lead to Disrupted Responses to Light in Diurnal Grass Rats (Arvicanthis niloticus)

The circadian system regulates daily rhythms of physiology and behavior. Although extraordinary advances have been made to elucidate the brain mechanisms underlying the circadian system in nocturnal species, less is known in diurnal species. Recent studies have shown that retinorecipient brain areas such as the intergeniculate leaflet (IGL) and olivary pretectal nucleus (OPT) are critical for the display of normal patterns of daily activity in diurnal grass rats (Arvicanthis niloticus). Specifically, grass rats with IGL and OPT lesions respond to light in similar ways to intact nocturnal animals. Importantly, both the IGL and OPT project to one another in nocturnal species, and there is evidence that these 2 brain regions also project to the superior colliculus (SC). The SC receives direct retinal input, is involved in the triggering of rapid eye movement sleep in nocturnal rats, and is disproportionately large in the diurnal grass rat. The objective of the current study was to use diurnal grass rats to test the hypothesis that the SC is critical for the expression of diurnal behavior and physiology. We performed bilateral electrolytic lesions of the SC in female grass rats to examine behavioral patterns and acute responses to light. Most grass rats with SC lesions expressed significantly reduced activity in the presence of light. Exposing these grass rats to constant darkness reinstated activity levels during the subjective day, suggesting that light masks their ability to display a diurnal activity profile in 12:12 LD. Altogether, our data suggest that the SC is critical for maintaining normal responses to light in female grass rats.

The blindside: impact of monocular occlusion on spatial attention

Monocular occlusion has been posited to reduce activation of the contralateral hemisphere ("Sprague effect"), thus inducing a contralateral spatial bias (toward the viewing eye). Healthy right-handed participants bisected horizontal lines during monocular eye viewing. Although subjects tended to deviate away from the viewing eye, only left-eye viewing deviated significantly right of midline. These results suggest that eye patching may induce an attentional compensation similar to that in hemianopic patients. Alternatively, increased activation of higher cortical regions mediating spatial attention in contralateral hemispace may be an adaptive response to decreased activation of its ipsilateral superior colliculus induced by contralateral eye patching.

Relationships between the superior colliculus and hippocampus: Neural and behavioral considerations

Theories of superior collicular and hippocampal function have remarkable similarities. Both structures have been repeatedly implicated in spatial and attentional behaviour and in inhibitory control of locomotion. Moreover, they share certain electrophysiological properties in their single unit responses and in the synchronous appearance and disappearance of slow wave activity. Both are phylogenetically old and the colliculus projects strongly to brainstem nuclei instrumental in the generation of theta rhythm in the hippocampal EEC

On the other hand, close inspection of behavioural and electrophysiological data reveals disparities. In particular, hippocampal processing mainly concerns stimulus ambiguity, contextual significance, and spatial relations or other subtle, higher order characteristics. This requires the use of largely preprocessed sensory information and mediation of poststimulus investigation. Although collicular activity must also be integrated with that of “higher” centres (probably to a varying degree, depending on the nature of stimuli being processed and the task requirements), its primary role in attention is more “peripheral” and specific in controlling orienting/localisation via eye and body movements toward egocentrically labelled spatial positions. In addition, the colliculus may exert a nonspecific influence in alerting higher centres to the imminence of information potentially worthy of focal attention. Nevertheless, it is noteworthy that collicular and hippocampal lesions produce deficits on similar tasks, although the type of deficit is usually different (often opposite) in each case. Functional overlap between hippocampus and colliculus (i.e., strategically synchronised or mutually interdependent activity) is virtually certain vis-à-vis stimulus sampling, for example in the acquisition of information via vibrissal movements and visual scanning. In addition, insofar as stimulus significance is a factor in collicular orienting mechanisms, the hippocampus — cingulate – cortex — colliculus pathway may play a significant role, modulating collicular responsiveness and thus ensuring an attentional strategy appropriate to current requirements (stimulus familiarity, stage of learning). A tentative “reciprocal loop” model is proposed which bridges physiological and behavioural levels of analysis and which would account for the observed degree and nature of functional overlap between the superior colliculus and hippocampus.

Postural muscle tone in the body axis of healthy humans

Across the entire human body, postural tone might play its most critical role in the body's axis because the axis joins the four limbs and head into a single functioning unit during complex motor tasks as well as in static postures. Although postural tone is commonly viewed as low-level, tonic motor activity, we hypothesized that postural tone is both tonically and dynamically regulated in the human axis even during quiet stance. Our results describe the vertical distribution of postural muscle tone in the neck, trunk, and hips of standing human adults. Each subject stood blindfolded on a platform that axially rotated the neck, trunk, or pelvis at 1 degrees /s and +/-10 degrees relative to the neutral position (i.e., facing forward). The measured resistance to axial rotation was highest in the trunk and lowest in the neck and was characterized by several nonlinear features including short-range stiffness and hysteresis. In half of the subjects, axial muscle activity was relatively constant during axial rotation, and in the other half, muscle activity was modulated by lengthening and shortening reactions, i.e., decreasing activity in lengthening muscles and increasing activity in shortening muscles, respectively. Axial resistance to rotation was reduced in subjects whose muscle activity was modulated. The results indicate that axial tone is modulated sensitively and dynamically, this control originates, at least in part, from tonic lengthening and shortening reactions, and a similar type of control appears to exist for postural tone in the proximal muscles of the arm.

The liabilities of mobility: a selection pressure for the transition to consciousness in animal evolution

The issue of the biological origin of consciousness is linked to that of its function. One source of evidence in this regard is the contrast between the types of information that are and are not included within its compass. Consciousness presents us with a stable arena for our actions-the world-but excludes awareness of the multiple sensory and sensorimotor transformations through which the image of that world is extracted from the confounding influence of self-produced motion of multiple receptor arrays mounted on multijointed and swivelling body parts. Likewise excluded are the complex orchestrations of thousands of muscle movements routinely involved in the pursuit of our goals. This suggests that consciousness arose as a solution to problems in the logistics of decision making in mobile animals with centralized brains, and has correspondingly ancient roots.

Decreases in the latency of smooth pursuit and saccadic eye movements produced by the "gap paradigm" in the monkey

The initiation of both pursuit and saccades was affected by the presence of a temporal gap between the disappearance of a fixated visual target and the appearance of a second, eccentric, target. For pursuit, the gap paradigm produced a modest (20 msec) decrease in latency. For saccades, the gap paradigm produced a similar modest decrease in the latency of some saccades, but also revealed a population of very short latency "express" saccades. The modest changes in the latency of pursuit and regular saccades displayed a similar dependence on gap duration, with the largest decreases produced by gaps of 200-300 msec. The gap paradigm did not produce "express" pursuit, even though express saccades could be elicited on interleaved trials.

Superior colliculus activity related to attention and to connotative stimulus meaning

Single-and multi-unit activity was recorded from cells in the superior colliculus of two awake monkeys (Macaca fascicularis). 32.5% of 366 investigated units responded while the animals attentively gazed at visual stimuli. 50% of these neurons responded to all stimuli presented, including stationary and moving light bars, whereas the other neurons only responded to specific stimuli like faces or food. The responses of a part of these neurons depended on the connotative stimulus meaning.

Catatonia: the tension insanity

A historical review of Kahlbaum's Catatonia is presented. He attributed the condition to organic cerebral disease. It is now best considered as a neuropsychiatric syndrome due to a wide variety of organic disease processes, manifest in catelepsy in a setting of an abnormal mental state, most commonly an affective disorder. Chronic catatonic states were common sequelae of encephalitis lethargica; this disease has now disappeared in epidemic form with a resulting fall in the incidence of catatonia in psychiatric hospitals. Acute catatonia, due to medical and particularly pharmacogenic causes, continues to occur in current psychiatric practice.

Where is the self? A neuroanatomical theory of consciousness

The enigmatic nature of the experience of self-awareness is examined in the light of recent discoveries and, on this basis, combined with inferences derived introspectively from the experience of the phenomenon itself; a specific physical locus of this experience within the human brains is deduced-proposed. The fundamental premise in this work is that whereever conscious self-awareness is generated, the neuronal structure(s) involved must continually have access to an extremely precise representation of information derived from the sense of vision plus a great variety of other kinds of information so as to permit it to make decisions regarding actions (movements and their implementation) that promote the survival and perpetuation of the biological system in which the self is generated. First, a definitve set of criteria that define most of the inputs to and operations carried out by the self-awareness entity were assembled. This ensemble of functions was then compared with the connections and possible roles of specific neuroanatomical structures described in published literature, particularly the recent literature and particularly that concerned with the sense of vision. It was discovered that only one brain structure receives the prerequisite information from the sense of vision plus information derived from cortical memory stores plus a variety of other relevant sources needed to generate a coherent sense of selfness. This structure is the superior colliculus of the tectum. The superior colliculi not only receive a highly precise retinotopic representation of inputs to the eyes, but also receive inputs from a great variety of other structures, including many areas of the cerebral cortex, vestibular inputs, auditory inputs, "affective" inputs, and inputs that putatively define the positions of the eyes and of the head. This information, it is deduced, not only allows this structure to generate a continuing synthesis of representations of the self-vs.-environment, but also allows a part of it to assess the significance (probable meaning) of these integrated inputs with respect to the selection of an implementation of actions that serve the interests of the physical structure in which the self-experience is generated. The function of memory in this system not only involves the continually updated representation of where the self is with respect to items and objects in its environment, but also provides means through which the relevance of recorded experiences representing the past may be caused to affect the decision-making process.(ABSTRACT TRUNCATED AT 400 WORDS)

Stupor: a review of 25 cases

Twenty-five cases of stupor referred to a psychiatric teaching hospital over 15 years are reviewed. Ten cases presented with a depressive syndrome, four cases with catatonic phenomena and a further 10 cases with established organic aetiology; one case was considered to be psychogenic in origin. The overall mortality was high (16%), attributable to the basic pathology. Compared with earlier series there was a reduction in cases with catatonic features with a corresponding increase in the proportion of organic cases.

Basal ganglia outflow pathways and circling behaviour in the rat

The role of efferents in substantia nigra pars reticulata in the mediation of circling behaviour in the rat has been studied by means of lesions designed to interrupt these pathways or to damage nigral projection areas. The behavioural model used was the circling rodent with a prior 6-hydroxydopamine lesion of the left nigro-striatal pathway in which amphetamine induced ipsiversive rotation and apomorphine induced contraversive rotation. Removal of the left fronto-parietal cortex caused only a transient decrease in drug-induced rotation. An electrolytic lesion of the left, right or both parafascicular thalamic nuclei did not alter circling behaviour. Electrolytic lesioning of the left ventromedial thalamus decreased apomorphine-induced contraversive circling whereas a lesion of the right ventromedial thalamus decreased amphetamine-induced ipsiversive rotation. Bilateral electrolytic lesions of the ventromedial thalamus did not alter drug-induced circling. Unilateral or bilateral electrolytic lesioning of the medial superior colliculus did not alter the rotational response to apomorphine or amphetamine. However, an electrolytic lesion interrupting the dorsal tegmental decussation reduced apomorphine-induced circling but not amphetamine-induced circling. That a critical role for the nigro-thalamic and nigro-tectal pathways is not involved in the mediation of circling behaviour was confirmed by placing knife cuts so as to separate these structures from the substantia nigra; such lesions failed to alter the contraversive rotation induced by the ipsilateral injection of muscimol into substantia nigra pars reticulata. Electrolytic lesions of the ipsilateral nucleus reticularis gigantocellularis or kainic acid lesions of the ipsilateral nucleus tegmenti pedunculopontinus did not alter drug-induced circling in animals with a prior 6-hydroxydopamine nigral lesion. In contrast, an ipsilateral lesion of the midbrain periaqueductal grey matter and adjacent midbrain reticular formation (the angular complex) decreased apomorphine-induced contraversive rotation in such animals, while bilateral lesions reduced both apomorphine-and amphetamine-induced circling; in each case the postural component of rotation was abolished. Unilateral kainic acid lesions of the angular complex in naive animals caused ipsiversive rotation which was enhanced by apomorphine. Unilateral kainic acid lesions of the angular complex with an ipsilateral 6-hydroxydopamine nigral lesion caused reversal of the previous contraversive rotation to apomorphine, and enhanced amphetamine-induced ipsiversive rotation.(ABSTRACT TRUNCATED AT 400 WORDS)

Decerebrate rigidity produced in cats by focal stereotactic radiofrequency lesions

A method of producing decerebrate rigidity in cats by means of a radio frequency current was developed. Adequate control of the extent an shape of the lesions necessitated a preliminary investigation of the relationship between the intensity and duration of current, the size of the lesion, and the tissue impedance before and after destruction; this was performed on guinea pigs. The mesencephalic reticulum in cats was identified by depth microelectrode recording and electrical stimulation. Unilateral, midline, and combined stereotactic radiofrequency lesions were made. The anatomical location, the pathological characteristics, and the physiological significance of the lesions with regard to the production of decerebrate rigidity and of the other clinical reactions of the animals are discussed.

Differential autonomic responses of autistic and normal children

The autonomic responses of 10 autistic and 10 normal children were compared using auditory stimuli varying in social relevance. Consistent differences in heart rate response and skin conductance level were found between the groups. The results suggest that the autistic subjects exhibited deficits in psychophysiological reactivity to a range of environmental stimuli. Findings are discussed in terms of the information-processing capabilities of autistic children, and probable physiological correlates. Implications for treatment are considered.

Pathophysiology and pharmacotherapy of spasmodic torticollis: a review

The few existing neuropathological, neurochemical, and neuropharmacological studies have shed little light on the pathophysiology of spasmodic torticollis (ST). The relevance of experimental ST in animals and drug-induced ST in man to idiopathic ST is unclear. Most pharmacotherapeutic endeavors have focused on drugs affecting basal ganglia function. Unfortunately, problems of sample size, clinical heterogeneity of patient population, research design, objective evaluation of response, documentation of key data, and adequacy of duration of follow-up make interpretation of published results difficult. Because of the heterogeneity of ST, investigations aimed at establishing a neurotransmitter profile for each patient by observing the acute response to a test dose of drugs affecting cholinergic, dopaminergic, serotonergic, and gamma-aminobutyric acid systems may provide a more rational basis to the selection of treatment.

The effect of decerebrate rigidity on the intracranial pressure: an experimental study

The mechanical effect of acute decerebrate rigidity upon the ICP and the mechanisms underlying the relationship between them have been investigated with experiments performed on 26 cats. It has been shown that: a) Extreme rigidity of the peripheral musculature with or without partial activation of the trunkal muscles produces no change in ICP, b) the simultaneous elevation of the intra-thoracic and intra-abdominal pressures is the factor primarily operative in raising and maintaining the elevated ICP, c) when cerebrovascular homeostasis is already defective a subsidiary but not unimportant role is played by the elevation of the systemic arterial pressure, d) under conditions of normal brain elastance mild and short-lasting spasms produce no effect on the ICP. In an animal, however, in which the brain elastance had been increased by inflating a small air-filled balloon, similar spasms produced a marked increase in ICP.

Visual cortical areas mediating form discrimination in the cat

Cats were trained pre- and/or postoperatively on flux and pattern discriminations, and were examined in a series of visuomotor tests which measured attention and orientation to, and following and localization of stationary and moving stimuli, in a free situation and in a perimetry test. Cortical lesions were placed in areas 17 and 18, or in the middle and posterior suprasylvian gyri and sulci--areas 19, 20, 21, 7 and lateral suprasylvian cortex (LSA), as delineated by cyto- and myeloarchitecture, and by electrophysiological mapping. After removal of all of area 17 and up to 90-95% of 18, postoperative learning of flux and pattern discriminations is at a high level, although in some cases slowed. Visuomotor behavior is normal. Such lesions result in severe atrophy only of laminae A, A1 and C in the lateral geniculate nuclear complex (LGNd). The neuronal systems for perceiving and discriminating simple, large planimetric patterns and forms, and for mediating visually guided behavior characteristic of this species lie outside of areas 17-18. The cortices primarily responsible for form discrimination in the cat include those in the suprasylvian gyri and sulci. After lesions which removed areas 19, 20, 21 and LSA, sparing most of 17-18, form discriminations based on orientation or shape were prolonged or absent. Although these animals showed slow tracking and poor depth judgment, the visual fields were full and they had good sensory and perceptive capacity as seen in normal flux and near normal pattern (gratings) discrimination. Such lesions result in severe atrophy in lateral and inferior pulvinar complex. Although these nuclei receive visual input primarily from the superficial laminae of the superior colliculus and certain nuclei of the pretectum, both areas 19 and LSA receive a dual input from pulvinar and parts of LGNd. Whether these marked deficits in form discrimination after suprasylvian lesions are due to involvement of certain crucial areas of this extensive cortex, or whether all are involved in some integrated fashion, is not yet completely clear. Removal of 19, 21 and parts of LSA are followed by similar (but somewhat less marked) deficits of both retention and learning. Lesion in area 20 alone (cortical target of the lateral pulvinar) leaves retention of preoperatively learned discriminations intact but results in prolonged initial learning. Previous work by the present authors has shown similar deficits in form discrimination in the cat after lesions in the pretectum-superior colliculus. These data, together with the present findings appear to support the hypothesis that the midbrain-pulvinar-cortical pathways provide the first stage in simple, coarse form perception and discrimination in this species.

Visual localization and discrimination in squirrel monkeys with bilateral lesions of the superior colliculus

This study measured the effects of superior colliculus (SC) lesions on skill at localizing stationary or moving objects, and on ability to discriminate between objects which differed in pattern or brightness in squirrel monkeys. Bilateral electrolytic lesions of the SC were made in 8 monkeys (EXP group); the lesions in 5 (SC group) were restricted essentially to the SC (22-25% damaged), the other 3 had additional unilateral damage to the midbrain reticular formation (10 to 14% damage to SC). The control group (N = 15) consisted of 9 unoperated, 3 sham-operated, and 3 lesioned-control monkeys. General cage behavior of the EXP group was not significantly changed as a result of the lesions. Eye movements were observed in all monkeys with SC lesions. Pupillary constrictions to light were also present except for a temporary unilateral mydriasis (two cases). On tests which measured reaction time, localization ability, and brightness discrimination, performance between the SC and control groups did not differ significantly. The SC group compared with controls, however, required more total trials to learn to criterion the pattern discrimination (p less than .05), and made significantly fewer correct choices (p less than .02) at the middle delay interval of the delayed response test. The two groups did not differ significantly at the shorter or longer delays. With regard to the possible neural mechanism, it is suggested that the SC of primates may influence level of arousal and contribute to ability to discriminate visual detail.

Patterns of decerebration in infants and children: defects in homeostasis and sequelae

Sixty-four infants and children showing signs of decerebrate rigidity admitted to a paediatric unit have been studied. Cases of head injury, myelomeningocoele, and tumours were excluded from the series. The aetiological factors causing decerebration in the remainder fell into four main groups: infections, hypoxia, metabolic disease, and intracranial haemorrhage. Increased intracranial pressure was diagnosed in 87%. Defects in homeostasis occurred in 75%, respiratory abnormalities were present in 66%, cardiovascular in 33%, hypothermia in 30%, and hyponatraemia in 17%. Early recognition and treatment of raised intracranial pressure and defects in homeostasis are of the utmost importance if morbidity and mortality are to be minimized. There was a 31% mortality from the acute illness: 30% of the survivors were normal at follow-up examination; the remainder showed varying degrees of handicap. The severity of decerebration showed no correlation with aetiology or prognosis. The study shows that a wide range of disorders can lead to the clinical picture of decerebration in the young child, and that the prognosis is probably much better than in adults showing the same symptoms and signs.