Changes In Neural Responses Research Articles

Social and emotional attachment in the neural representation of faces

To dissociate the role of visual familiarity from the role of social and emotional factors in recognizing familiar individuals, we measured neural activity using functional magnetic resonance imaging (fMRI) while subjects viewed (1) faces of personally familiar individuals (i.e. friends and family), (2) faces of famous individuals, and (3) faces of strangers. Personally familiar faces evoked a stronger response than did famous familiar faces and unfamiliar faces in areas that have been associated with ‘theory of mind’, and a weaker response in the amygdala. These response modulations may reflect the spontaneous activation of social knowledge about the personality and attitudes of close friends and relatives and the less guarded attitude one has around these people. These results suggest that familiarity causes changes in neural response that extend beyond a visual memory for a face.

Relation between neuronal morphology and electrophysiology in the Kainate lesion model of Alzheimer's Disease

This paper describes a computational and statistical study of the influence of morphological changes on the electrophysiological response of neurons from an animal model of Alzheimer's Disease (AD). We combined experimental morphological data from rat hippocampal CA1 pyramidal cells with a well-established model of active membrane properties. Dendritic morphology and the somatic response to simulated current clamp conditions were then compared for cells from the control and the AD group. The computational approach allowed us to single out the influences of neuromorphology on neuronal response by eliminating the effects of active channel variability. The results did not reveal a simple relationship between morphological changes associated with AD and changes in neural response. However, they did suggest the existence of more complex than anticipated relationships between dendritic morphology and single-cell electrophysiology.

Neurotrophin-4/5 Alters Responses and Blocks the Effect of Monocular Deprivation in Cat Visual Cortex during the Critical Period

The mechanisms underlying changes in neural responses and connections in the visual cortex may be studied by occluding one eye during a critical period in early postnatal life. Under these conditions, neurons in the visual cortex rapidly lose their responses to the deprived eye and ultimately lose many of their inputs from that eye. Cats at the peak of the critical period received infusions of exogenous neurotrophin NT-4/5 into primary visual cortex beginning before a short period of monocular deprivation. Within areas affected by NT-4/5, cortical cells remained responsive to the deprived eye, and maps of ocular dominance were no longer evident using intrinsic-signal optical imaging. Cortical cells also became broadly tuned for stimulus orientation and less responsive to visual stimulation through either eye. These effects required at least 48 hr exposure to the neurotrophin and were specific for trkB, because they were not seen with the trkA or trkC ligands NGF or NT-3. Even after neurons had already lost their responses to the deprived eye, subsequent NT-4/5 infusion could restore them. The NT-4/5 effects were not seen after the critical period. Together, these results suggest that trkB activation during the critical period may promote promiscuous connections independent of correlated activity.

12. Sex and brain development

Consistent with the importance of reproductive behavior for survival of the species, the gonadal steroids are major regulators of neural function and brain development. Investigation of these regulatory effects has revealed both mechanisms and principles that underlie emergent behavioral properties. First, activational effects of gonadal steroids comprise both acute, signal transduction-mediated and classical, intracellular receptor-mediated actions, the latter including modulation of the synthesis of the synthetic and metabolic enzymes for neurotransmitters, neuropeptides, neuroeffector receptors, and second messengers. Second, gonadal steroids create a context that influences both formation of neurocircuitry and acute neural response. These actions are largely inferred from three types of observations: structural and functional sexual dimorphisms; changes in neural response during reproductive endocrine change (e.g. the ovulatory cycle); and modulation of response to hormone manipulation (e.g. castration). In fact, all stages of neuronal development—neurogenesis, growth, migration, differentiation, and synaptic organization—are modulated by gonadal steroids. Third, gonadal steroids organize the brain during critical developmental windows. Androgen blockade, for example, alters 5-HT1A receptor m-RNA but not GABA receptor subunit expression during the last prenatal week, while the opposite is observed during the fourth postnatal week. Fourth, the effects of gonadal steroids are context dependent and differ as a function of environment, prior exposure, age, and genotypic characteristics. Studies of the effects of gonadal steroids on behavior promise to help answer the critical question in human behavioral endocrinology: Why do different individuals respond differently to ostensibly the same stimulus?

Feature-based attention influences motion processing gain in macaque visual cortex.

Changes in neural responses based on spatial attention have been demonstrated in many areas of visual cortex, indicating that the neural correlate of attention is an enhanced response to stimuli at an attended location and reduced responses to stimuli elsewhere. Here we demonstrate non-spatial, feature-based attentional modulation of visual motion processing, and show that attention increases the gain of direction-selective neurons in visual cortical area MT without narrowing the direction-tuning curves. These findings place important constraints on the neural mechanisms of attention and we propose to unify the effects of spatial location, direction of motion and other features of the attended stimuli in a 'feature similarity gain model' of attention.

Distance modulation of neural activity in the visual cortex.

Humans use distance information to scale the size of objects. Earlier studies demonstrated changes in neural response as a function of gaze direction and gaze distance in the dorsal visual cortical pathway to parietal cortex. These findings have been interpreted as evidence of the parietal pathway's role in spatial representation. Here, distance-dependent changes in neural response were also found to be common in neurons in the ventral pathway leading to inferotemporal cortex of monkeys. This result implies that the information necessary for object and spatial scaling is common to all visual cortical areas.

The role of the spinothalamic tract in the plastic changes in somatosensory thalamus and cortex caused by inflammation

Dr. Guilbaud describes 15 years of work in her laboratory in which she and her colleagues examined plastic changes in the responses of neurons in the rat somatosensory thalamus and cerebral cortex following the induction of an inflammatory pain state, either by injection of Freund's adjuvant into the tail or of carrageenan into the hindpaw. The goals of this work included: a demonstration of changes in neural responses that parallel the development of hyperalgesia and allodynia in the inflamed area; a description of changes in response to stimulation of uninflamed areas that might help explain secondary hyperalgesia; investigation of the question of whether a specific joint pain system exists; and exploration of how altered joint input might dominate cortical responses atthe expense of other somatic inputs. I will elaborate on the first three of these from the perspective of experiments on primate spinothalamic tract neurons in my laboratory.

Effects of larval diet and larval age on the responsiveness of taste neurones of Spodoptera littoralis to sucrose

Previous experiments with a bean-based artificial diet have shown that the responsiveness of peripheral sensilla of larvae of Spodoptera littoralis to sucrose is influenced by the age of the larvae within a stadium. This paper investigates that effect with another artificial diet (wheat-based) and with plant material from two host plants, cabbage and seedling wheat. The present results show that the three diets influence the responsiveness of neurones to sucrose and sodium chloride. The effects of the diets on the day-to-day responses and the within-day responses to both stimuli are illustrated. The neural response of the lateral maxillary styloconic sensillum to sucrose correlates with larval weight during the first 3 days of the final stadium, but no comparable relationship was found with sodium chloride, suggesting that different mechanisms operate for different stimuli. The mechanisms which may be involved in the day-to-day changes in neural responses to sucrose are discussed.

A combined 2-deoxyglucose and neurophysiological study of primate somatosensory cortex.

The metabolic activity pattern produced in the primary somatosensory cortex (SI) of primates by repetitive delivery of a tactile stimulus is distinctly patchy. The functional significance of these patches, however, remains obscure. This investigation sought to determine the correlation between neural and metabolic activity produced by tactile stimuli and to evaluate the relationship, if any, between the neural activity and metabolic patches evoked by similar stimuli. Experiments were undertaken in which extracellular microelectrode recordings were carried out in animals that subsequently underwent a 2-deoxyglucose (2DG) study. Three types of relations were identified. First, the receptive fields (RF) and modality properties of neurons sampled in locations at which patches of metabolic label were found matched the "place" and "modal" properties of the stimulus used to produce 2DG labeling. Second, in cortical locations where the RF and modality properties of the sampled neurons differed from either the place or modal properties of the stimulus used to evoke the 2DG label, no above-background increases in metabolic labeling were found. Finally, in some cortical locations at which the receptive field and modality properties of the neurons matched those of the 2-deoxyglucose mapping stimulus, no above-background increases in metabolic labeling were found. This outcome leads us to suggest that moment-to-moment changes in neural responsivity, which might remain undetected by conventional receptive field mapping methods, contribute to the patchy pattern of metabolic activity visualized by the 2-deoxyglucose method.

Efferent inhibition of auditory-nerve responses: dependence on acoustic-stimulus parameters.

Electrical stimulation of the crossed olivocochlear bundle in anesthetized cats reduces auditory-nerve responses (N1) if the acoustic stimuli are at low sound-pressure levels but does not produce detectable changes in neural responses for click stimuli more than 60 to 70 dB above visual-detection level for N1. When the sound-pressure levels of high-frequency (10 000-Hz) and low frequency (400-Hz) transient acoustic stimuli were matched according to a physiological criterion, the neural response to the high- frequency stimulus was reduced more by olivocochlear bundle stimulation than the response to the low-frequency stimulus. These result, suggest certain characteristics for the mechanisms which influence the activity of single auditory-nerve fibers.