Impairment in preattentive processing among patients with hypertension revealed by visual mismatch negativity

Assessment of Cognition in Hypertensives and Normotensives: A Comparative P300 Study

Background: Hypertension is an established risk factor for dementia, and the prevalence of hypertension and dementia is rising. Current tests to diagnose cognitive dysfunction at an early stage lack sensitivity and specificity. Recently event-related potentials (ERPs) have gained much attention in diagnosing cognitive dysfunction and are independent of the education status of the subject. This study was done to find any cognitive deficits in the hypertensive population with electrophysiological evidence, which might open the doors for the need to screen the population at an earlier stage so that the population can be prevented from dementia.

Methods: Some 31 middle-aged (18-65 years) hypertensives were compared with 31 age, sex, education, and handedness matched normotensives about cognition by neuropsychometric test battery including Hindi Mini-mental Status Examination (HMSE), Hindi Montreal Cognitive Assessment (MoCA), choice reaction time (CRT), and auditory event-related potentials.

Results: Hypertensives and normotensives differed significantly concerning P300 potentials’ latency (Fz and Cz P300 latencies: p-value: 0.001), and this change was correlated well with the duration of diastolic blood pressure (BP) (r-value: 0.670). The remaining tests, HMSE, Hindi MoCA, and CRT, were dependent on the education status of the patient.

Conclusions: The effect of hypertension on cognitive impairment is evident and can be proved early in its pre-clinical stage using ERPs. Early identification can help in specifying high-risk individuals. ERPs have great potential in screening and diagnosing and can also help in assessing cognition as a reliable tool to show the effect of treatments/interventions on cognitive defects.

Automatic detection of the duration of visual static and dynamic stimuli

The perception of the passing of time is fundamental to conscious experience. The duration of a sensory stimulus is one of its defining attributes, but it is not clear how this is encoded in the brain. This work explores whether the duration of a visual stimulus is an attribute that the brain can automatically adapt to and use to predict future stimulus durations. Visual mismatch negativity (vMMN) is an ERP component elicited, even when the stimuli are unattended, when an 'unexpected' visual stimulus appears amongst a series of expected stimuli in an 'oddball' paradigm. As such vMMN has been suggested to show that the violation of a pattern in a sequence has been automatically detected. To date, vMMN has only been measured to differences in the visual durations of static on/off stimuli, placed near to the centre of the visual field. Our study measures vMMN to test whether duration is encoded automatically for static stimuli against a blank background and moving stimuli against a static background, whilst attention is directed to a different spatial location using a continuous, attention demanding task. VMMN elicited in response to the shorter duration for both stimuli shows that the brain detects the differences of duration even in the absence of focussed spatial attention. For the motion stimulus a larger difference in duration was needed. We conclude that duration is encoded automatically in the visual cortex and is an attribute that can be adapted to, and form the basis of predictions.

Visual mismatch negativity: a predictive coding view

An increasing number of studies investigate the visual mismatch negativity (vMMN) or use the vMMN as a tool to probe various aspects of human cognition. This paper reviews the theoretical underpinnings of vMMN in the light of methodological considerations and provides recommendations for measuring and interpreting the vMMN. The following key issues are discussed from the experimentalist's point of view in a predictive coding framework: (1) experimental protocols and procedures to control "refractoriness" effects; (2) methods to control attention; (3) vMMN and veridical perception.