Temporal preparation in patients with Neglect syndrome

The right parietal cortex has been widely associated with a spatial orienting network. Its damage frequently produces the Neglect syndrome consisting in deficits in spatial attention to the left hemifield. Neglect has also been related to temporal deficits (such as the estimation of the duration of a stimulus or the discrimination of two stimuli that occur at the same spatial location but at different time intervals). Such attentional deficits have been much less studied in the temporal as compared to the spatial domain. The current research focused on the study of temporal attention processes in patients with Neglect syndrome, specifically, on temporal preparation. We recruited 10 patients with Neglect syndrome, 10 patients without Neglect syndrome, as well as 11 healthy individuals. Each participant completed an experimental task which measures three main temporal preparation effects described in the literature: Temporal orienting and Foreperiod effects (both related to control mechanisms and prefrontal areas) and Sequential effects (automatic in nature and related to parietal and subcortical structures). The results showed a deficit in the sequential effects only in those patients who suffered from Neglect syndrome. The results suggest a causal relation between Neglect syndrome and the automatic mechanisms of temporal preparation. Since our sample of Neglect patients had suffered lesions mainly in the parietal cortex, the results are discussed taking into account the role of the parietal lobe in the processing of time and the models explaining sequential effects

La corteza parietal derecha ha sido asociada con una red de orientación espacial. Su daño produce frecuentemente el síndrome de Heminegligencia que consiste en déficits en la atención espacial al hemicampo izquierdo. Dicho síndrome también se ha relacionado con déficits temporales (como la estimación de la duración de un estímulo o la discriminación de dos estímulos que ocurren en la misma ubicación espacial pero en diferentes intervalos de tiempo). Sin embargo, tales déficits atencionales han sido menos estudiados en el ámbito temporal que en el espacial. La presente investigación pretende el estudio de los procesos de atención temporal en pacientes con síndrome de Heminegligencia. Se reclutaron 10 pacientes con síndrome de Heminegligencia, 10 pacientes sin Heminegligencia y 11 individuos sanos. Cada participante realizó una tarea experimental que estudia tres efectos principales de preparación temporal descritos en la literatura: Orientación temporal y Foreperiod (ambos relacionados con mecanismos de control y áreas prefrontales) y Efectos secuenciales (de naturaleza más automática y relacionados con estructuras parietales y subcorticales). Los resultados mostraron un déficit en los efectos secuenciales únicamente en los pacientes con Heminegligencia. Esto sugiere una relación causal entre el síndrome de Heminegligencia y los mecanismos automáticos de preparación temporal. Dado que nuestra muestra de pacientes heminegligentes había sufrido lesiones principalmente en la corteza parietal, los resultados se discuten teniendo en cuenta el papel del lóbulo parietal en el procesamiento del tiempo, y en el marco de los modelos que explican los efectos secuenciales

Conscious perception in patients with prefrontal damage.

We are conscious and verbally report some of the information reaching our senses, although a big amount of information is processed unconsciously. There is no agreement about the neural correlates of consciousness, with low-level theories proposing that neural processing on primary sensory brain regions is the most important neural correlate of consciousness, while high-level theories propose that activity within the fronto-parietal network is the key component of conscious processing (Block, 2009). Contrary to the proposal of high-level theories, patients with prefrontal lobe damage do not present clinical symptoms associated to consciousness deficits. In the present study, we explored the conscious perception of near-threshold stimuli in a group of patients with right prefrontal damage and a group of matched healthy controls. Results demonstrated that perceptual contrast to perceive the near-threshold targets was related to damage to the right dorsolateral prefrontal cortex, and with reduced integrity of the ventral branch of the right superior longitudinal fascicule (SLF III). These results suggest a causal role of the prefrontal lobe in conscious processing.

Target bottom-up strength determines the extent of attentional modulations on conscious perception.

A sufficient level of alerting, bottom-up stimulus strength, and attention have been proposed as important pre-requisites for conscious perception (Dehaene et al. in Trends Cogn Sci 10:204-211, 2006). The combination of different levels of each of these processes might differentially bias the access to consciousness, so that the impact of a specific factor on conscious access would depend on the levels of the other factors. To explore this possibility, we measured how the interaction between different levels of (phasic and tonic) alerting, stimulus bottom-up activation, and endogenous spatial attention, influences conscious perception. We observed that endogenous spatial attention affected conscious perception mainly when target bottom-up strength was low, by improving perceptual sensitivity and making the response criterion stricter. Attention-driven increases of perceptual sensitivity (without variations in response criterion) were also observed for higher levels of bottom-up strength, but only when tonic alerting decreased. Phasic alerting boosted perceptual sensitivity independently of target bottom-up strength, even though it differently affected response bias, yielding a more liberal response criterion when target bottom-up strength increases. These results suggest that a more exhaustive approach to the study of conscious perception should consider the interaction of the multiple factors that are susceptible to modulate perceptual consciousness, rather than studying their effects in isolation.

Effectiveness of a neuropsychological treatment for confabulations after brain injury: A clinical trial with theoretical implications.

Confabulators consistently generate false memories without intention to deceive and with great feelings of rightness. However, to our knowledge, there is currently no known effective treatment for them. In order to fill this gap, our aim was to design a neuropsychological treatment based on current theoretical models and test it experimentally in 20 confabulators sequentially allocated to two groups: an experimental and a control group. The experimental group received nine sessions of treatment for three weeks (three sessions per week). The sessions consisted of some brief material that participants had to learn and recall at both immediate and delayed time points. After this, patients were given feedback about their performance (errors and correct responses). Pre- and post-treatment measurements were recorded. Confabulators in the control group were included in a waiting list for three weeks, performed the pre- and post- measurements without treatment, and only then received the treatment, after which a post-treatment measurement was recorded. This applied to only half of the participants; the other half quit the study prematurely. Results showed a significant decrease in confabulations and a significant increase in correct responses in the experimental group; by contrast, patients in the control group did not improve during the waiting list period. Only control group patients who subsequently received the treatment after serving as controls improved. The effects of the treatment were generalized to patients' everyday lives, as reported by relatives, and persisted over time. This treatment seems to be effective and easy to implement and consequently of clinical interest. Moreover, it also has theoretical implications regarding the processes related to the genesis and/or maintenance of confabulations. In particular, results point to a deficit in early stages of memory retrieval with the preservation of later strategic monitoring processes. Specifically, some of the processes involved may include selective attention or early conflict detection deficits. Future research should test these hypotheses.