Role In Decision-making Process Research Articles

Brain Activation during Mental Maze Solving

Background: So-called Porteus mazes are used to investigate prefrontal cortex (PFC) functioning in normal subjects and patients with different neuropsychiatric disorders. Here we present data confirming the involvement of the PFC for the first time by means of functional magnetic resonance imaging (fMRI). To minimize motor-related activation, mental mazes were used. Methods: Mazes as well as pseudo-mazes without any bifurcations were presented to 49 healthy participants during fMRI scans. Results: Both, mazes as well as pseudo-mazes, activated a large network from visual to parietal regions, reflecting the dorsal stream of visual information processing. Mazes but not pseudo-mazes also activated bilateral areas of the PFC indicating their special role in decision processes. In addition, although no motor response was required during maze performance, both tasks activated subcortical and cortical motor areas. Conclusions: These tasks are suitable for investigating and specifying PFC functioning and its impairment in psychiatric disorders such as schizophrenia. In addition, mental mazes might be a suitable task for the investigation of patients with motor disturbances.

Memory Strength and Repetition Suppression: Multimodal Imaging of Medial Temporal Cortical Contributions to Recognition

Declarative memory permits an organism to recognize stimuli that have been previously encountered, discriminating them from those that are novel. One basis for recognition is item memory strength, which may support the perception of stimulus familiarity. Though the medial temporal lobes are known to be critical for declarative memory, at present the neural mechanisms supporting perceived differences in memory strength remain poorly specified. Here, functional MRI (fMRI) and anatomically constrained magnetoencephalography (MEG) indexed correlates of graded memory strength in the human brain, focusing on medial temporal cortex. fMRI revealed a decrease in medial temporal cortical activation that tracked parametric levels of perceived memory strength. Anatomically constrained MEG current estimates revealed that strength-dependent signal reductions onset within 150-300 ms. Memory strength appears to be rapidly signaled by medial temporal cortex through repetition suppression (activation reductions), providing a basis for the subjective perception of stimulus familiarity or novelty.

Bleaching kinetics of artificial visual pigments with modifications near the ring-polyene chain connection.

Absorbance difference spectra were recorded at 20 degrees C from 30 ns to milliseconds after photolysis of lauryl maltoside suspensions of artificial visual pigments derived from 9-cis isomers of 5-ethylretinal, 8,16-methanoretinal (a 6-s-trans-bicyclic analogue), or 5-demethyl-8-methylretinal. In all three pigments, the earliest intermediate that was detected had the characteristics of a mixture of bathorhodopsin and a blue-shifted intermediate, BSI, which is the first decay product of bathorhodopsin in bovine rhodopsin. The first decays resolved on the nanosecond time scale were the formation of the lumirhodopsin analogues. Subsequent decays were able to be fit with a mechanistic scheme which has been shown to apply to both membrane and detergent suspensions of rhodopsin. Large increases were seen in the amount of metarhodopsin I which appeared after photolysis of 5-ethylisorhodopsin and the bicyclic isorhodopsin analogue, while 5-demethyl-8-methylisorhodopsin more closely followed native rhodopsin in decaying through meta I380, a 380 nm absorbing precursor to metarhodopsin II. In addition to forming more metarhodopsin I, the bicyclic analogue stabilized the metarhodopsin I-metarhodopsin II equilibrium similarly to what has been previously reported for 9-demethylrhodopsin in detergent, introducing the possibility that the bicyclic analogue could similarly be defective in transducin activation. These observations support the idea that long after initial photolysis, structural details of the retinylidene chromophore continue to play a decisive role in processes leading to the activated form, metarhodopsin II.

The Role of Decision Processes in Conscious Recollection

Dual-process models of recognition memory posit a rapid retrieval process that produces a general sense of familiarity and a slower retrieval process that produces conscious recollections of prior experience. The remember/know paradigm has been used to study the subjective correlates of these two processes, with remember judgments assumed to index conscious recollection and know judgments assumed to index familiarity. Recently, a two-criterion signal detection model has been proposed as an alternative account of this paradigm. This model assumes only a single memory process with a criterion separating remember from know responses. This report presents an empirical test of the model's critical prediction that manipulations that influence criterion placement should influence both remember and know judgments. An experiment confirmed this prediction, demonstrating that subjects who were told that 70% of the test items were study items produced more remember and know responses than subjects who were told that 30% of the test items were study items.

The role of decision processes in remembering and knowing

Participants in recognition memory studies are now often asked to partition recognized items into ones that are accompanied by some recollective experience (those they remember) and ones that are not so accompanied (but which they know were previously encountered). Rather than detecting separate memory systems, such attempts to distinguish between remembering and knowing are better understood as a division of positive recognition responses into those that lie above a second decision criterion (remember) and those that do not (know). As such, the amount of memory associated with knowing is strongly dependent on the placement of the decision criteria. A meta-analysis of published data and a simple experiment tested predictions from the decision process analysis of remember/know responses.

Ecological responses to reductions in freshwater supply and quality in South Africa’s estuaries: Lessons for management and conservation

Fresh water, a fundamental element of all estuarine ecosystems, is South Africa's most limited natural resource. Recent projections indicate that by the year 2020 the country will be utilizing all its exploitable freshwater sources. Steeply increasing demands by a rapidly growing population on this limited commodity have already resulted in a severe reduction of water supplies to natural users such as estuaries - this trend is predicted to increase in the future. Concurrent with exces- sive water abstraction, poor land husbandry (e.g. soil erosion) in many catchment basins and pollution (e.g. salinization) in return flows have led to a serious deterioration in water qual- ity. In contrast, a review of estuarine responses to varying flow regimes stresses the strong dependence of local systems on riverine fresh water inputs of adequate quantity and quality. Freshwater dependence is i.a. expressed in: flooding events that scour accumulated sediments, riverine nutrient input to drive estuarine phyto- and zooplankton production, axial sa- linity gradients that increase habitat and species diversity, and maintenance of open tidal inlets that prevent salinity and temperature extremes and facilitate larval exchange, fish mi- grations and tidal flushing of salt marshes. Thus, estuarine conservation will have to encompass management of rivers and watersheds and play an increasingly political role in decision processes concerning water allocations among 'hu- man' and 'natural' users.

Transesophageal echocardiography in the awake elderly patient: Its role in the clinical decision-making process

To assess the impact on the management and safety of transesophageal echocardiography (TEE) in the elderly population, the results and limitations of this technique were retrospectively analyzed in 88 patients. TEE was indicated whenever the transthoracic approach was not diagnostic or was inconsistent with the clinical setting. The most frequent clinical indications were to investigate the source of emboli, assess valvular regurgitation, and identify valvular vegetations. In 72 patients (82%) TEE significantly influenced management decisions. In selected patients TEE avoided the use of more invasive diagnostic procedures. Adverse effects included occasional premature atrial or ventricular beats (11 patients), sinus bradycardia (six patients), and protracted nausea (one patient). We conclude that in elderly patients with cardiovascular diseases, TEE plays a significant role in the decision-making process without adding a significant risk.

Intercategory distance and categorization times: Effects of negative-probe relatedness

Meyer ( Journal of Experimental Psychology , 1973, 99 , 124–133) found that subjects were faster to determine whether or not a stimulus word was a member of either of two prespecified categories if the categories were close rather than distant in meaning. In this paper a reanalysis of the data casts doubt on Meyer's interpretation in terms of memory structure and favors a model which emphasizes the role of decision-making processes in categorization and the flexibility of subjects' strategies in dealing with the task. An experiment is reported which offers limited support for both models. Some difficulties of investigating semantic memory are discussed.