The area that deals with visual space explored by the eyes is the lateral intraparietal (LIP) area, which was defined on the basis of its connections to the frontal eye fields, lateral pulvinar, and the superior colliculus. This chapter proposes that LIP represents a priority map that can be used by both the oculomotor system to choose a saccade goal when a saccade is appropriate, and by the visual system to determine the locus of visual attention. Thus, rather than serving a dedicated sensorimotor function, the same signal can serve as an intention or attention signal, depending on the recipient area and the behavioral context. Furthermore, the genesis of the spikes is irrelevant to their interpretation: Thus, spikes evoked by the abrupt onset of a visual stimulus can drive saccades, and spikes evoked by the plan for a memory-guided delayed saccade can drive visual attention. LIP sums all the signals that project to it to create the priority map.
Abstract How do we learn to establish associations between arbitrary visual cues (like a red light) and movements (like braking the car)? We investigated the neural correlates of visuomotor association learning in the monkey mid-lateral cerebellum. Here we show that, during learning but not when the associations were overlearned, individual Purkinje cells reported the outcome of the monkey’s most recent decision, an error signal, which was independent of changes in hand movement or reaction time. At the population level, Purkinje cells collectively maintained a memory of the most recent decision throughout the entire trial period, updating it after every decision. This error signal decreased as the performance improved. Our results suggest a role of mid-lateral cerebellum in visuomotor associative learning and provide evidence that cerebellum could be a generalized learning system, essential in non-motor learning as well as motor learning.
SUMMARY To identify brain lesions most often associated with cerebral visual impairment (CVI) after neonatal encephalopathy and to evaluate the prognostic value of MRI for visual outcome, the authors reviewed visual assessments and brain MRI of 80 infants and young children with documented perinatal hypoxic‐ischaemic and/or haemorrhagic insults. MRIs were classified according to the severity of lesions at the optic radiations and at the visual cortex; visual acuity was tested with the acuity card procedure. Among the 48 children found to have a CVI, 42 had moderate to severe lesibns of the optic radiations and 19 had lesions of the visual cortex. In both cases visual acuity was statically correlated with MRI grading, but the damage at the optic radiations was the better predictor. Early detection of abnormal MR findings in the visual cortex and. especially, at the optic radiations may indicate which infants with neonatal encephalopthy should receive longitudinal visual assessment and specific rehabilitation and educational management. RÉSUMÉ Corrélations entre les troubles cérébraux de la vision et les IRM chez les enfants avec encéphalopathie néonatale Dans le but d'identifier les lésions cérébrales le plus souvent associées à un trouble visucl cérébral (CVI) après une encéphalopathie néonatale ct d'evaluer la valeur pronostique de l'IRM pour le devenir visuel, les auteurs ont passé en revue l'évaluation visuclle et les IRM cérébrales de 80 nourrissons et jeunes enfants avec antécédents d'agression périnatale hypoxo‐ischémiquc et/ou hémorragiquc. Les IRM furent classées en fonction de la séverité des lésions dc radiations optiques et du cortex visuel; l'acuité visuelle fut appréciée par les échelles habituelles d'acuité. Parmi les 48 enfants avec CVI, 42 avaient des lésions modérées à sévères des radiations optiques et 42 avaienr des lésions du cortex visucl. Dans les deux cas, l'acuité visuclle était corrélée avec l'importancc des manifestations IRM mais l'atteinte des radiations optiques était le meilleur prédicteur. La détection précoce d'anomalies IRM du cortex visuel et, spécialement des radiations optiques, peut indiquer que les nourrissons avec encéphalopathie néonatale devraient bénéficier d'un suivi de la fonction visuelle, d'une rééducation spécifique et d'une prise en charge éducative. ZUSAMMENFASSUNG Korrelatkm zwischen cerebraler Sehstörung und Magnet Resonitanz Tomographic bei Kindern mit neonataler Enzeplialopathie Die Autoren untersuchten bei 80 Säuglingen und Klcinkindern mit dokumentierten perinatalen hypoxish‐ischämischen und/oder hämorrhagischen Insulten die visuellen Untersuchungs‐ und Hirn‐ MRI Befunde, urn Hirnläsionen, die nach neonataler Enzephalopathie am haufigstcn mit cerebralen Sehstörungen (CVI) einhergehen, zu bestimmen und urn den prognostischen Wert des Hirn‐MRI für den visuellen Outcome zu beurteilen. Die MRIs wurden nach dem Schweregrad der Läsionen an den Sehbahnen und am visuellen Cortex klassifiziert; die Sehschärfe wurde anhand der Acuity Card Procedure festgestellt. Von den 48 Kindern, bei denen eine CVI diagnostiziert wurde, hatten 42 mäßige bis schwere Läsionen an den Sehbahnen und 19 Läsionen des visuellen Cortex. In beiden Fällen bestand eine statistische Korrelation zwischen Sehschärfe und MRI‐Grading, die Schädigung der Sehbahnen hatte aber die bessere prognostische Aussagekraft. Durch frühzeitige Erkennung abnormer MRI Befunde im visuellen Cortex und besondcr an den Sehbahnen kann festgelegt werden, welche Kinder mit neonataler Enzephalopathie langfristigc Sehprüfungen, sowie besondere Rehabilitation und Schulförderung bekommen sollten. RESUMEN Correlación entre la alteración visual cerebral y la imagen por resonancia magnética en niños con encepfalopatia neonatal Para identificar lesiones cerebrales mayormente asociadas a alteración visual cerebral (AVC) después de una encefalopatiá neonatal y para evaluar el valor pronóstico de la IRM con respecto al curso de la visión, los autores revisaron las evaluaciones visuales y la IRM de 80 lactantes y niños pequeños que habian sufrido, documentadamente, en la época perinatal una hipoxic‐isquemia y/o una haemorragia cerebrales. La IRM se clasificó de acuerdo con la gravedad de las lesiones a nivel de las rediaciones ópticas y del córtex visual; la agudeze visual se examinó por el procedimiento de las targetas de agudeza. Entre los 48 niños con AVC, 42 tenian lesiones de moderadas a graves de las radiaciones ópticas y 19 del córtex visual. En ambos casos la agudeza visual estaba estadísticamente correlacionada con el grado de alteración de la IRM, pero la alteración de las radiaciones ópticas constituía un mejor predictor. La detectión precoz de anomalías IRM en el córtex visual, y especialmente en las radiaciones ópticas, puede indicar qué niños con encefalopatía neonatal deben recibir una evaluatión visual longitudinal, así como una rehabilitación específica y manejo educativo.
A hallmark of visual cortical neurons is their selectivity for stimulus pattern features, such as color, orientation, or shape. In most cases this feature selectivity is hard-wired, with selectivity manifest from the beginning of the response. Here we show that when a task requires that a monkey distinguish between patterns, V4 develops a selectivity for the sought-after pattern, which it does not manifest in a task that does not require the monkey to distinguish between patterns. When a monkey looks for a target object among an array of distractors, V4 neurons become selective for the target ∼50 ms after the visual latency independent of the impending saccade direction. However, when the monkey has to only make a saccade to the spatial location of the same objects without discriminating their pattern, V4 neurons do not distinguish the search target from the distractors. This selectivity for stimulus pattern develops roughly 40 ms after the same neurons’ selectivity for basic pattern features like orientation or color. We suggest that this late-developing selectivity is related to the phenomenon of feature attention and may contribute to the mechanisms by which the brain finds the target in visual search.
The purpose of saccadic eye movements is to facilitate vision, by placing the fovea on interesting objects in the environment. Eye movements are not made for reward, and they are rarely restricted. Despite this, most of our knowledge about the neural genesis of eye movements comes from experiments in which specific eye movements are rewarded or restricted. Such experiments have demonstrated that activity in the lateral intraparietal (LIP) area of the monkey correlates with the monkey's planning of a memory-guided saccade or deciding where, on the basis of motion information, to make a saccade. However, other experiments have shown that neural activity in LIP can easily be dissociated from the generation of saccadic eye movements, especially when sophisticated behavioral paradigms dissociate the monkey's locus of attention from the goal of an intended saccade. In this study, we trained monkeys to report the results of a visual search task by making a nontargeting hand movement. Once the task began, the monkeys were entirely free to move their eyes, and rewards were not contingent on the monkeys making specific eye movements. We found that neural activity in LIP predicted not only the goal of the monkey's saccades but also their saccadic latencies.
Previous studies have shown that subjects require less time to process a stimulus at the fovea after a saccade if they have viewed the same stimulus in the periphery immediately prior to the saccade. This extrafoveal preview benefit indicates that information about the visual form of an extrafoveally viewed stimulus can be transferred across a saccade. Here, we extend these findings by demonstrating and characterizing a similar extrafoveal preview benefit in monkeys during a free-viewing visual search task. We trained two monkeys to report the orientation of a target among distractors by releasing one of two bars with their hand; monkeys were free to move their eyes during the task. Both monkeys took less time to indicate the orientation of the target after foveating it, when the target lay closer to the fovea during the previous fixation. An extrafoveal preview benefit emerged even if there was more than one intervening saccade between the preview and the target fixation, indicating that information about target identity could be transferred across more than one saccade and could be obtained even if the search target was not the goal of the next saccade. An extrafoveal preview benefit was also found for distractor stimuli. These results aid future physiological investigations of the extrafoveal preview benefit.
Abstract Although the cerebellum has been implicated in simple reward-based learning recently, the role of complex spikes (CS) and simple spikes (SS), their interaction and their relationship to complex reinforcement learning and decision making is still unclear. Here we show that in a context where a non-human primate learned to make novel visuomotor associations, classifying CS responses based on their SS properties revealed distinct cell-type specific encoding of the probability of failure after the stimulus onset and the non-human primate’s decision. In a different context, CS from the same cerebellar area also responded in a cell-type and learning independent manner to the stimulus that signaled the beginning of the trial. Both types of CS signals were independent of changes in any motor kinematics and were unlikely to instruct the concurrent SS activity through an error based mechanism, suggesting the presence of context dependent, flexible, multiple independent channels of neural encoding by CS and SS. This diversity in neural information encoding in the mid-lateral cerebellum, depending on the context and learning state, is well suited to promote exploration and acquisition of wide range of cognitive behaviors that entail flexible stimulus-action-reward relationships but not necessarily motor learning.
Abstract Although the cerebellum has been traditionally considered to be exclusively involved in motor control and learning, recent anatomical and clinical studies suggest that it may also have a role in cognition. However, no electrophysiological evidence exists to support this claim. Here we studied the activity of simple spikes of hand-movement related Purkinje cells in the mid-lateral cerebellum when monkeys learned to associate a well-learned right or left-hand movement with one of two visual symbolic cues. The cells had distinctly different discharge patterns between an overtrained symbol-hand association and a novel symbol-hand association although the kinematics of the movement did not change between the two conditions. The activity change was not related to the pattern of the visual symbols, the hand making the movement, the monkeys’ reaction times or the novelty of the visual symbols. We suggest that mid-lateral cerebellum is involved in higher-order cognitive processing related to learning a new visuomotor association. One Sentence Summary Hand-movement related Purkinje neurons in midlateral cerebellum, which discharge during an overtrained visuomotor association task, change their activity when the monkey has to associate the same movements with new cues, even though the kinematics of the movements do not change.
