Neural correlates of auditory recognition memory in the primate dorsal temporal pole

Temporal pole (TP) cortex is associated with higher-order sensory perception and/or recognition memory, as human patients with damage in this region show impaired performance during some tasks requiring recognition memory ( Olson et al. 2007 ). The underlying mechanisms of TP processing are largely based on examination of the visual nervous system in humans and monkeys, while little is known about neuronal activity patterns in the auditory portion of this region, dorsal TP (dTP; Poremba et al. 2003 ). The present study examines single-unit activity of dTP in rhesus monkeys performing a delayed matching-to-sample task utilizing auditory stimuli, wherein two sounds are determined to be the same or different. Neurons of dTP encode several task-relevant events during the delayed matching-to-sample task, and encoding of auditory cues in this region is associated with accurate recognition performance. Population activity in dTP shows a match suppression mechanism to identical, repeated sound stimuli similar to that observed in the visual object identification pathway located ventral to dTP ( Desimone 1996 ; Nakamura and Kubota 1996 ). However, in contrast to sustained visual delay-related activity in nearby analogous regions, auditory delay-related activity in dTP is transient and limited. Neurons in dTP respond selectively to different sound stimuli and often change their sound response preferences between experimental contexts. Current findings suggest a significant role for dTP in auditory recognition memory similar in many respects to the visual nervous system, while delay memory firing patterns are not prominent, which may relate to monkeys' shorter forgetting thresholds for auditory vs. visual objects.

F-VEPs IN ZEN MEDITATION

The observation of the inner-light perception in deep Zen meditation14 has aroused our attention. Based on the recording of F-VEPs (flash visual evoked potentials), this study was thus designed to investigate the characteristics of visual nervous pathway for the Zen-meditation practitioners (experimental group), in comparison with that for the normal, healthy subjects (control group). Flash stimuli were applied before, during and after meditation/relaxation in experimental/control subjects. We focused on the F-VEPs at the occipital site Oz, central site Cz and frontal site Fz. Our results show that amplitudes of late latency components N3-P3 and P3-N4 at Oz decrease for the experimental subjects during meditation, whereas they increase in the control group. Both Cz and Fz amplitudes increase during meditation, yet decrease during relaxation for the control group. The latencies of some components were increased under relaxation in control group, yet little variation (except P2) is observed in the meditators. We also applied discrete wavelet transform to F-VEPs to analyze the frequency components. Our results showed that delta, theta and alpha components increased during meditation at some specific time periods. According to our findings, Zen meditation induces particular effects on the visual nervous system and cortex that are distinct from the normal relaxation.

Violations of sensorimotor theories of visual experience

Although the sensorimotor account is a significant step forward, it cannot explain experiences of entoptic phenomena that violate normal sensorimotor contingencies but nonetheless are perceived as visual. Nervous system structure limits how they can be interpreted. Neurophysiology, combined with a sensorimotor theory, can account for space constancy by denying the existence of permanent representations of states that must be corrected or updated.