Behavioural brain research
-
Traditional anatomical/behavioral classifications suggest that rats and opossums have simple motor systems and are impoverished with respect to their ability to make prehensile movements. Nevertheless, the motor system in rats and opossums represent extremes in relative size and complexity suggesting that a behavioral analysis of the movement competencies of these species will provide insights into the significance of such anatomical differences. This paper examines the movements that the two species use in catching crickets and in reaching for food items. ⋯ Thus, the skilled movements of both species are more complex than is generally recognized and the greater complexity of the rat movements parallels their more complex motor system. These results are discussed in relation to anatomical differences in the motor system and, specifically, to differences in the terminal fields of the pyramidal tract. It is concluded that the motor abilities of nonprimate mammals have been vastly underrated.
-
Historical Article
Hebb's concept of synaptic plasticity and neuronal cell assemblies.
Both in vertebrates and in invertebrates the study of processes of plasticity in nervous systems have led to consistent models of molecular mechanisms for the so-called Hebb's synapse. Changes of synaptic efficacy will lead to changes in the properties of assemblies of nerve cells--as seen today the correlates of purport. Donald Hebb's view of the characteristics of such assemblies appears farsighted.
-
The red nucleus (RN) is a prominent structure in the motor system of mammals and is thought to play a role in the control of limb movement. In the rat, there are contradictory reports concerning its role in controlling movements of the paw and digits in grasping food in skilled reaching tasks. Some studies report severe impairments in the effectiveness of limb movement and impairments in grasping movements, whereas other studies report only mild impairments. ⋯ This change results in a very rapid grasp and an absence of a pause in limb transport during grasping. These impairments and the 'release' of the grasp response suggests that the RN may provide the tonus or supporting framework that momentarily immobilizes the limb so that arpeggio and grasping movements can occur. It is suggested that the function of the RN more generally may be to provide a tonic framework against which the motor cortex can produce more fractionated movements.
-
We have previously shown that spatial memory changes following experimental traumatic brain injury (TBI) include long-term changes that are (1) 'overt': detected by routine behavioral assessments, or (2) 'covert': undetected in the absence of a secondary pharmacological challenge, such as by the cholinergic antagonist, scopolamine. Our objective in this study was to extend this finding by characterizing the time course of recovery of overt and covert spatial memory performance following two magnitudes of experimental TBI. The Morris water maze was used to assess cognitive performance. ⋯ These data suggest three distinct stages of functional recovery: (1) the initial period when overt deficits are present, (2) a period following recovery from overt deficits within which covert deficits can be reinstated by a pharmacological challenge, and (3) a period following recovery from both overt and covert deficits. Covert deficits can persist long after the recovery of overt deficits and, like other neurological deficits, the rate of recovery is dependent on the magnitude of TBI. Finally, spatial memory deficits can occur in the absence of light microscopic evidence of cell death in the hippocampus.
-
Impairment of cognitive abilities is a frequent and significant sequelae of traumatic brain injury (TBI). The purpose of this experiment was to examine the generality of the cognitive deficits observed after TBI. The performance of three tasks was evaluated. ⋯ On days 11-15 following injury, injured (n = 9) and sham-injured (n = 8) rats were trained on a constant-start version of the Morris water maze that has the animals begin the maze from a fixed start position on each trial. Additional injured (n = 8) and sham-injured (n = 8) animals were trained on days 11-15 after injury on the standard (i.e. using variable start positions) version of the Morris water maze. The results of this experiment revealed that performance of the passive avoidance and the constant-start version of the Morris water maze were not impaired by fluid percussion TBI.(ABSTRACT TRUNCATED AT 250 WORDS)