Biomedical subjects

M C Davidson

Publications and source records attributed to M C Davidson.

8 recordsLinked to original sources

PubMed2004

Differential cingulate and caudate activation following unexpected nonrewarding stimuli.

This study examined the effects of varying the predictability of nonrewarding events on behavior and neural activation using a rapid mixed-trial functional magnetic resonance imagery (fMRI) design. Twelve adult subjects were scanned with echo planar imaging during performance of a visual detection task where the probability of events (target and nontarget) varied. This task included expected and unexpected nonrewarding events (expected target, unexpected nontarget, and omission of target) in a design that closely parallels studies of dopamine function and reward processing in the alert monkey. We predicted that activation in dopamine-rich areas of the forebrain would behave like the animal literature shows that dopamine neurons in the midbrain behave. Specifically, we predicted increased activity in these regions when an unexpected event occurred and decreased activity when an expected event was omitted. Two main regions, the anterior cingulate and dorsal striatum, showed this pattern. The response in these regions was distinguished by enhanced anterior cingulate activity following the occurrence of an unexpected event and greater suppression of caudate activity following the omission of an expected event. These results suggest that neural activity within specific dopamine-rich brain regions can be modulated by violations in the expectation of nonrewarding events and that the direction of the modulation depends on the nature of the violations.

Adult↗

PubMed2003

Imaging the developing brain with fMRI.

Advancements in magnetic imaging techniques have revolutionized our ability to study the developing human brain in vivo. The ability to noninvasively image both anatomy and function in healthy volunteers, including young children, has already enhanced our understanding of brain and behavior relations. The application of these techniques to developmental research offers the opportunity to further explore these relationships and allows us to ask questions about where, when and how cognitive abilities develop in relation to changes in underlying brain systems. It is also possible to explore the contributions of maturation versus learning in the development of these abilities through cross-sectional and longitudinal research involving training and intervention procedures. Current imaging methodologies, in conjunction with new and rapidly evolving techniques, hold the promise of even greater insights into developmental issues in the near future. These methodologies and their application to development and learning are discussed in the current paper.

Adult↗

PubMed2003

Parametric manipulation of conflict and response competition using rapid mixed-trial event-related fMRI.

In the current study we examined the influence of preceding context on attentional conflict and response competition using a flanker paradigm. Nine healthy right-handed adults participated in a rapid mixed trial event-related functional magnetic resonance imaging (fMRI) study, in which increasing numbers of either compatible or incompatible trials preceded an incompatible trial. Behaviorally, reaction times on incompatible trials increased as a function of the number of preceding compatible trials. Several brain regions showed monotonic changes to the preceding context manipulation. The most common pattern was observed in anterior cingulate, dorsolateral prefrontal, and superior parietal regions. These areas showed an increase in activity for incompatible trials as the number of preceding compatible trials increased and a decrease in activity for incompatible trials as the number of preceding incompatible trials increased. Post hoc analysis showed that while the MR signal in the anterior cingulate and dorsolateral prefrontal regions peaked before the superior parietal region, the dorsolateral prefrontal MR signal peaked early and remained at this level. These findings are consistent with the conflict monitoring theory that postulates that the anterior cingulate cortex detects or monitors conflict, while PFC is involved in control adjustments that may then lead to modulation of superior parietal cortex in top-down biasing of attention.

Adult↗

PubMed2000

Local infusion of scopolamine into intraparietal cortex slows covert orienting in rhesus monkeys.

There is accumulating evidence to suggest that cholinergic neurotransmission may play an important role in visuospatial attention, but the brain sites at which acetylcholine modulates attention are not well understood. The present work tested the hypothesis that the cholinergic influences within the intraparietal cortex are necessary for normal attentional shifting (covert orienting) in nonhuman primates. Two rhesus monkeys were trained to perform a visual, cued target detection task for liquid reinforcement. The animals pressed a lever to produce a visual display in which a central fixation point was flanked by two circles. Shortly after fixation was established, one of the circles brightened (cue), and a target appeared subsequently within one of the circles. Detection was signaled by a manual response and the reaction time to the appearance of the target was recorded. Four types of trials were presented. For valid cue trials, the cue and target were at the same spatial location; for invalid cues, cue and target were in opposite hemifields; for double cues, both cues were brightened but the target appeared in either the left or right circle; in no-cue trials, the cue was omitted. We localized the intraparietal region by recording attention-related, cellular activity with intracerebral microelectrodes. Among visually responsive cells in this area, valid cues presented to the receptive fields of visual neurons enhanced the responses to target stimuli in about half the cells and inhibited those responses in the remainder. In addition, some cells showed longer response latencies to invalid cues than to valid cues. We then infused scopolamine into attention-related activity sites and assessed its effect on performance. Scopolamine produced a dose-dependent increase in reaction times and decrease in performance accuracy that lasted more than 1 h. Neither vehicle injections in the same locations nor scopolamine outside the physiologically defined area produced any significant change in behavior. Under our conditions of measurement, we conclude that activity mediated by muscarinic cholinergic receptors within the intraparietal cortex is necessary for normal covert orienting.

Animals↗

PubMed1999

Scopolamine slows the orienting of attention in primates to cued visual targets.

The cholinergic agonist nicotine facilitates visuospatial attention shifting, but the role of muscarinic cholinergic drugs in this behavior is unclear. In order to establish the generality of cholinergic action in attention shifting, we administered the muscarinic antagonist scopolamine to two rhesus monkeys trained to perform a cued target detection (Posner) task. In this task, monkeys signaled the detection of a peripheral visual target by releasing a switch and their reaction times were measured. The location of the target's appearance was preceded by a cue that was either valid (target and cue in the same spatial location), invalid (target and cue to opposite hemifields), spatially uninformative (cues in both hemifields, target to one hemifield), or omitted altogether. Scopolamine produced a dose-dependent increase in all reaction times and a decrease in accuracy. The slowing was most prominent for valid cues in either visual field. However, slowing did not occur in trials whose cues lacked spatial information, or in tasks in which attention was directed to events at the fixation point, whether or not peripheral distractors were present. These results provide additional support for the hypothesis that acetylcholine plays a key role in reflexive attention shifting to peripheral visual targets.

Analysis of Variance↗

PubMed1998

Toward a functional analysis of the basal ganglia.

Parkinson patients were tested in two paradigms to test the hypothesis that the basal ganglia are involved in the shifting of attentional set. Set shifting means a respecification of the conditions that regulate responding, a process sometimes referred to as an executive process. In one paradigm, upon the appearance of each stimulus, subjects were instructed to respond either to its color or to its shape. In a second paradigm, subjects learned to produce short sequences of three keypresses in response to two arbitrary stimuli. Reaction times were compared for the cases where set either remained the same or changed for two successive stimuli. Parkinson patients were slow to change set compared to controls. Parkinson patients were also less able to filter the competing but irrelevant set than were control subjects. The switching deficit appears to be dopamine based; the magnitude of the shifting deficit was related to the degree to which 1-dopa-based medication ameliorated patients' motor symptoms. Moreover, temporary withholding of medication, a so-called off manipulation, increased the time to switch. Using the framework of equilibrium point theory of movement, we discuss how a set switching deficit may also underlie clinical motor disturbances seen in Parkinson's disease.

Aged↗

PubMed1997

Effects of altering brain cholinergic activity on covert orienting of attention: comparison of monkey and human performance.

Experiments were conducted to elucidate the role of the cholinergic neurotransmitter system in arousal and the orienting of attention to peripheral targets. Rhesus monkeys and humans fixated a visual stimulus and responded to the onset of visual targets presented randomly in two visual field locations. The target was preceded by a valid cue (cue and target at the same location), an invalid cue (cue and target to opposite locations), a double cue (cues to both spatial locations, target to one), or, the cue was omitted (no-cue, target to either location). Reaction times (RTs) to the onset of the target were recorded. For monkeys, systemic injections of nicotine (0.003-0.012 mg/kg) or atropine (0.001-0.01 mg/kg), but not saline control injections, reduced mean RTs for all trials, indicating general behavioral stimulation. In addition, nicotine significantly reduced RTs for invalid trials but had little additional effect on those for valid, double, or no-cue trials. Virtually identical effects were observed for human chronic tobacco smokers in performing the same task following cigarette smoking. Injections of atropine in monkeys had no effect on RTs for valid or invalid trials but significantly slowed RTs in double-cue trials that did not require the orienting of attention. These results suggest that in both species, the nicotinic cholinergic system may play a role in automatic sensory orienting. In addition, the muscarinic system may play a role in alerting to visual stimuli in monkeys.

Adolescent↗

PubMed1994

Arousal systems.

Recent advances in neural and behavioural pharmacology, and in intracellular recording suggest that arousal during the awake state may be regulated by multiple, interdependent neurotransmitter systems that originate in the brainstem or hypothalamus, and project to subcortical and cortical sites. We discuss efforts to determine the mechanisms by which these systems extent their effects, and the roles that they play in the control of arousal.

Animals↗