The effect of face inversion on activity in human neural systems for face and object perception.
The differential effect of stimulus inversion on face and object recognition suggests that inverted faces are processed by mechanisms for the perception of other objects rather than by face perception mechanisms. We investigated the face inversion using functional magnetic resonance imaging (fMRI). The principal effect of face inversion on was an increased response in ventral extrastriate regions that respond preferentially to another class of objects (houses). In contrast, house inversion did not produce a similar change in face-selective regions. Moreover, stimulus inversion had equivalent, minimal effects for faces in in face-selective regions and for houses in house-selective regions. The results suggest that the failure of face perception systems with inverted faces leads to the recruitment of processing resources in object perception systems, but this failure is not reflected by altered activity in face perception systems. (+info)
The cerebral haemodynamics of music perception. A transcranial Doppler sonography study.
The perception of music has been investigated by several neurophysiological and neuroimaging methods. Results from these studies suggest a right hemisphere dominance for non-musicians and a possible left hemisphere dominance for musicians. However, inconsistent results have been obtained, and not all variables have been controlled by the different methods. We performed a study with functional transcranial Doppler sonography (fTCD) of the middle cerebral artery to evaluate changes in cerebral blood flow velocity (CBFV) during different periods of music perception. Twenty-four healthy right-handed subjects were enrolled and examined during rest and during listening to periods of music with predominant language, rhythm and harmony content. The gender, musical experience and mode of listening of the subjects were chosen as independent factors; the type of music was included as the variable in repeated measurements. We observed a significant increase of CBFV in the right hemisphere in non-musicians during harmony perception but not during rhythm perception; this effect was more pronounced in females. Language perception was lateralized to the left hemisphere in all subject groups. Musicians showed increased CBFV values in the left hemisphere which were independent of the type of stimulus, and background listeners showed increased CBFV values during harmony perception in the right hemisphere which were independent of their musical experience. The time taken to reach the peak of CBFV was significantly longer in non-musicians when compared with musicians during rhythm and harmony perception. Pulse rates were significantly decreased in non-musicians during harmony perception, probably due to a specific relaxation effect in this subgroup. The resistance index did not show any significant differences, suggesting only regional changes of small resistance vessels but not of large arteries. Our fTCD study confirms previous findings of right hemisphere lateralization for harmony perception in non-musicians. In addition, we showed that this effect is more pronounced in female subjects and in background listeners and that the lateralization is delayed in non-musicians compared with musicians for the perception of rhythm and harmony stimuli. Our data suggest that musicians and non-musicians have different strategies to lateralize musical stimuli, with a delayed but marked right hemisphere lateralization during harmony perception in non-musicians and an attentive mode of listening contributing to a left hemisphere lateralization in musicians. (+info)
Unilateral neglect and disambiguation of the Necker cube.
Three groups of patients (right brain-damaged patients with or without left neglect, and left brain-damaged patients) and a group of healthy subjects, matched for age and educational level to the three groups of patients, were asked to report which of the two frontal surfaces of Necker cubes oriented in four different ways looked, at first sight, nearer to the viewer. The extent to which, and the way in which, disambiguation of the apparent perspective of Necker cubes occurred was found to vary across the four orientations and to be different in left-neglect patients compared with subjects of the other three groups. With normal subjects, the disambiguating factor is suggested to be a disposition to perceive the upper surface, which is nearly orthogonal to the frontal plane, as external to the cube. This would result from a navigation of the observer's spatial attention towards its target along a particular path that is altered in patients suffering from left neglect. It is suggested that comparison of the paths followed by the attentional vectors of normal subjects and left-neglect patients is potentially fruitful for a better understanding of the brain's normal mechanisms of spatial attention and of unresolved issues concerning the perception of the Necker cube. (+info)
Contralateral deafness following unilateral suboccipital brain tumor surgery in a patient with large vestibular aqueduct--case report.
A 68-year-old female developed contralateral deafness following extirpation of a left cerebellopontine angle epidermoid cyst. Computed tomography showed that large vestibular aqueduct was present. This unusual complication may have been caused by an abrupt pressure change after cerebrospinal fluid release, which was transmitted through the large vestibular aqueduct and resulted in cochlear damage. (+info)
The role of retinal waves and synaptic normalization in retinogeniculate development.
The prenatal development of the cat retinogeniculate pathway is thought to involve activity-dependent mechanisms driven by spontaneous waves of retinal activity. The role of these waves upon the segregation of the dorsal lateral geniculate nucleus (LGN) into two eye-specific layers and the development of retinotopic mappings have previously been investigated in a computer model. Using this model, we examine three aspects of retinogeniculate development. First, the mapping of visual space across the whole network into projection columns is shown to be similar to the mapping found in the cat. Second, the simplicity of the model allows us to explore how different forms of synaptic normalization affect development. In comparison to most previous models of ocular dominance, we find that subtractive postsynaptic normalization is redundant and divisive presynaptic normalization is sufficient for normal development. Third, the model predicts that the more often one eye generates waves relative to the other eye, the more LGN units will monocularly respond to the more active eye. In the limit when one eye does not generate any waves, that eye totally disconnects from the LGN allowing the non-deprived eye to innervate all of the LGN. Thus, as well as accounting for normal retinogeniculate development, the model also predicts development under abnormal conditions which can be experimentally tested. (+info)
Development and organization of ocular dominance bands in primary visual cortex of the sable ferret.
Thalamocortical afferents in the visual cortex of the adult sable ferret are segregated into eye-specific ocular dominance bands. The development of ocular dominance bands was studied by transneuronal labeling of the visual cortices of ferret kits between the ages of postnatal day 28 (P28) and P81 after intravitreous injections of either tritiated proline or wheat germ agglutinin-horseradish peroxidase. Laminar specificity was evident in the youngest animals studied and was similar to that in the adult by P50. In P28 and P30 ferret kits, no modulation reminiscent of ocular dominance bands was detectable in the pattern of labeling along layer IV. By P37 a slight fluctuation in the density of labeling in layer IV was evident in serial reconstructions. By P50, the amplitude of modulation had increased considerably but the pattern of ocular dominance bands did not yet appear mature. The pattern and degree of modulation of the ocular dominance bands resembled that in adult animals by P63. Flat mounts of cortex and serial reconstructions of layer IV revealed an unusual arrangement of inputs serving the two eyes in the region rostral to the periodic ocular dominance bands. In this region, inputs serving the contralateral eye were commonly fused along a mediolateral axis, rostral to which were large and sometimes fused patches of ipsilateral input. (+info)
Humour appreciation: a role of the right frontal lobe.
Humour occupies a special place in human social interactions. The brain regions and the potential psychological processes underlying humour appreciation were investigated by testing patients who had focal damage in various areas of the brain. A specific brain region, the right frontal lobe, most disrupted the ability to appreciate humour. The individuals with damage in this brain region also reacted less, with diminished physical or emotional responses (laughter, smiling). Performance on the humour appreciation tests used were correlated in a distinct pattern with tests assessing cognitive processes. The ability to hold information in mind (working memory) was related to both verbal (jokes) and non-verbal (cartoon) tests of humour appreciation. In addition, the demands of the specific type of humour test were related in a logical manner to cognitive processes, verbal humour being associated with verbal abstraction ability and mental shifting and cartoon humour being related to the abilities to focus attention to details and to visually search the environment. The ability of the right frontal lobe may be unique in integrating cognitive and affective information, an integration relevant for other complex human abilities, such as episodic memory and self-awareness. (+info)
Neglect after right insular cortex infarction.
BACKGROUND AND PURPOSE: Case reports have shown an association between right insular damage and neglect. The aim of this study was to examine the incidence of neglect among patient groups with right or left insular infarction. METHODS: We examined neglect in 9 right-handed subjects with insular stroke as evidenced by CT and/or MRI scans (4 with right insular and 5 with left insular cerebrovascular accident) between 4 and 8 weeks after acute stroke with tests of visual, tactile, and auditory perception. RESULTS: Compared with patients with left insular lesions, patients with right insular lesions showed significant neglect in the tactile, auditory, and visual modalities. CONCLUSIONS: The right insular cortex seems to have a role in awareness of external stimuli, and infarction in this area may lead to neglect in multisensory modalities. (+info)