Lesions of Periaqueductal Gray Dissociate-Conditioned Freezing From Conditioned Suppression Behavior in Rats

It is commonly assumed that suppression of an ongoing behavior is an indirect measure of freezing behavior. We tested whether conditioned suppression and freezing are the same or distinct conditioned responses. Rats were trained to press a bar for food and then given fear-conditioning sessions in which a tone was paired with a foot shock (two pairings a day for 2 days). They then received either sham or electrolytic lesions of the periaqueductal gray (PAG). Post-training PAG lesions blocked freezing to the conditioned stimulus (CS), but had no effect on the suppression of operant behavior to the same CS. Thus, conditioned suppression and freezing, which both cause a cessation in activity, appear to be mediated by separate processes.     

Damage to the lateral and central, but not other, amygdaloid nuclei prevents the acquisition of auditory fear conditioning

It is well established that the amygdala plays an essential role in Pavlovian fear conditioning, with the lateral nucleus serving as the interface with sensory systems that transmit the conditioned stimulus and the central nucleus as the link with motor regions that control conditioned fear responses. The lateral nucleus connects with the central nucleus directly and by way of several other amygdala regions, including the basal, accessory basal, and medial nuclei. To determine which of these regions is necessary, and thus whether conditioning requires the direct or one of the indirect intra-amygdala pathways, we made lesions in rats of the lateral, central, basal, accessory basal, and medial nuclei, as well as combined lesions of the basal and accessory basal nuclei and of the entire amygdala. Animals subsequently underwent fear conditioning trials in which an auditory conditioned stimulus was paired with a footshock unconditioned stimulus. Animals that received lesions of the lateral or central nucleus, or of the entire amygdala, were dramatically impaired, whereas the other lesions had little effect. These findings show that only the lateral and central nuclei are necessary for the acquisition of conditioned fear response to an auditory conditioned stimulus.     

Language, perception, and the schematic representation of spatial relations

Schemas are abstract nonverbal representations that parsimoniously depict spatial relations. Despite their ubiquitous use in maps and diagrams, little is known about their neural instantiation. We sought to determine the extent to which schematic representations are neurally distinguished from language on the one hand, and from rich perceptual representations on the other. In patients with either left hemisphere damage or right hemisphere damage, a battery of matching tasks depicting categorical spatial relations was used to probe for the comprehension of basic spatial concepts across distinct representational formats (words, pictures, and schemas). Left hemisphere patients underperformed right hemisphere patients across all tasks. However, focused residual analyses using voxel-based lesion-symptom mapping (VLSM) suggest that (1) left hemisphere deficits in the representation of categorical spatial relations are difficult to distinguish from deficits in naming these relations and (2) the right hemisphere plays a special role in extracting schematic representations from richly textured pictures.     

Art produced by a patient with Parkinson's disease

Artists with neurological diseases sometimes produce remarkably appealing art. Here we present the art of a patient with Parkinson's disease, who demonstrated remarkable creativity and productivity well into the course of his disease. Despite his manifest motor impairments, he produced paintings and drawings with fluid sinuous movements. He also became preoccupied with his art in an unprecedented way, raising the possibility that his disease and medications were contributing to his creative drive.