A Model for the Origin of Motion Direction Selectivity in Visual Cortex

Motion perception is a vital part of our sensory repertoire in that it contributes to navigation, awareness of moving objects, and communication. Motion sense in carnivores and primates originates with primary visual cortical neurons selective for motion direction. More than 60 years after the discovery of these neurons, there is still no consensus on the mechanism underlying direction selectivity. This paper describes a model of the cat''s visual system in which direction selectivity results from the well-documented orientation selectivity of inhibitory neurons: inhomogeneities in the orientation preference map for inhibitory neurons leads to spatially asymmetric inhibition, and thus to direction selectivity. Stimulation of the model with a drifting grating shows that direction selectivity results from the relative timing of excitatory and inhibitory inputs to a neuron. Using a stationary contrast-reversing grating reveals that the inhibitory input is spatially displaced in the preferred direction relative to the excitatory input, and that this asymmetry leads to the timing difference. More generally, the model yields physiologically realistic estimates of the direction selectivity index, and it reproduces the critical finding with contrast-reversing gratings that response phase advances with grating spatial phase. It is concluded that a model based on intracortical inhibition can account well for the known properties of direction selectivity in carnivores and primates.SIGNIFICANCE STATEMENT Motion perception is vital for navigation, communication, and the awareness of moving objects. Motion sense depends on cortical neurons that are selective for motion direction, and this paper describes a model for the physiological mechanism underlying cortical direction selectivity. The essence of the model is that intracortical inhibition of a direction-selective cell is spatially inhomogeneous and therefore depends on whether a stimulus generates inhibition before or after reaching the cell''s receptive field: the response is weaker in the former than in the latter case. If the model is correct, it will contribute to the understanding of motion processing in carnivores and primates.     

Factors affecting rehabilitation and use of upper limb after stroke: views from healthcare professionals and stroke survivors

Background: Training of the upper limb (UL) is limited in stroke rehabilitation, and about 50% of stroke survivors do not regain useful function in their upper limb.

Objectives: This study explored what factors affect rehabilitation and use of upper limb after stroke from a stroke survivor and healthcare professional perspective to better understand low engagement in UL rehabilitation in the chronic stages of stroke.

Method: Eight chronic stroke survivors and 21 healthcare professionals took part in semi-structured interviews or in one of three focus groups, respectively.

Results: Thematic analysis revealed three main themes: Availability of resources, Healthcare professional–patient relationship, and Psychosocial factors. Availability of resources and Healthcare professional–patient relationship indicated that due to resource pressures and a lack of communication and education, positive upper limb rehabilitation behaviors (e.g. engaging and integrating the upper limb in daily activity) were not always established in the early stages post-stroke. Psychosocial factors illustrated the cognitive and psychological barriers to sustained engagement with upper limb rehabilitation.

Conclusion: The findings indicate that stroke survivors and healthcare professionals have very similar understandings of barriers to UL activity, and positive upper limb rehabilitation behaviors are not always established early in recovery post-stroke. Increased resources and healthcare professional–patient relationships seem key factors to establishing positive perceptions of UL rehabilitation. Addressing psychosocial issues and resource limitations may help sustain engagement with UL rehabilitation.     

Conceptual clarification of the playful engagement in social interaction of preschool-aged children with autism spectrum disorder (ASD)

Children with autism spectrum disorder (ASD) demonstrate limited playfulness. Their difficulty engaging in meaningful interaction with others renders playful engagement in social interactions a challenge. Although little direct evidence exists regarding the promotion of these children’s playful engagement, links can be established with many traits cited in play and social interaction studies. This paper presents the results of a conceptual clarification exercise regarding the key behaviours associated with the construct of playful engagement in preschool-aged children with ASD. Behaviours were identified based on hallmark deficits in early social interactions and play of children with ASD. The analysis revealed the following behaviours: positive affect, engagement, imitation, joint attention, initiation of social interaction, social responsiveness, flexibility, child’s laughter in funny situations and giving and reading non-verbal cues. In conclusion, a conceptually coherent stage has been set for exploring the literature regarding interventions to promote the playful engagement of preschool-aged children with ASD.     

Rapid Increase in Neural Conduction Time in the Adult Human Auditory Brainstem Following Sudden Unilateral Deafness

Individuals with sudden unilateral deafness offer a unique opportunity to study plasticity of the binaural auditory system in adult humans. Stimulation of the intact ear results in increased activity in the auditory cortex. However, there are no reports of changes at sub-cortical levels in humans. Therefore, the aim of the present study was to investigate changes in sub-cortical activity immediately before and after the onset of surgically induced unilateral deafness in adult humans. Click-evoked auditory brainstem responses (ABRs) to stimulation of the healthy ear were recorded from ten adults during the course of translabyrinthine surgery for the removal of a unilateral acoustic neuroma. This surgical technique always results in abrupt deafferentation of the affected ear. The results revealed a rapid (within minutes) reduction in latency of wave V (mean pre = 6.55 ms; mean post = 6.15 ms; p < 0.001). A latency reduction was also observed for wave III (mean pre = 4.40 ms; mean post = 4.13 ms; p < 0.001). These reductions in response latency are consistent with functional changes including disinhibition or/and more rapid intra-cellular signalling affecting binaurally sensitive neurons in the central auditory system. The results are highly relevant for improved understanding of putative physiological mechanisms underlying perceptual disorders such as tinnitus and hyperacusis.     

Managing parrot bite injuries to the hand: not just another animal bite

Bites and scratches are common injuries, frequently sustained from humans, dogs and cats. Exotic pet-related harm however is an important and increasingly emerging class of injury. Whilst the principles of prompt and thorough medical assessment, antibiotics and potential surgical washout and debridement apply, exotic pet wounds require further consideration. Standard antibiotic prophylaxis with amoxicillin/clavulanic acid (also known as co-amoxiclav) is not sufficient for the pathogens transmitted by parrot bites. We illustrate the importance of adequate consideration of microbiological pathogens with a case report of an open finger fracture resulting from a parrot bite. We intend this to be a valuable resource for healthcare professionals in their effective management of such injuries.Level of Evidence: V