Functional MRI of working memory and selective attention in vibrotactile frequency discrimination

Viktig studie som nevner hvordan vibrasjoner på huden påvirker tilsvarende område i hjernen og hvilken relasjon dette har til hukommelse og kinestetisk oppmerksomhet. De kaller det vibrotactile memory. Denne bekrefter også at 25Hz aktiverer Meissner corpulses første og fremst. Nevner også at tidperspektivet i stimuleringen er viktig siden det aktiverer bilateralt insula (har med prosessering av følelser å gjøre). Den nevner også at hjernens «default network» dempes når vi blir oppmerksomme på vibrasjon, ganske likt det som skjer når vi mediterer.

Focal lesions of the frontal, parietal and temporal lobe may interfere with tactile working memory and attention. To characterise the neural correlates of intact vibrotactile working memory and attention, functional MRI was conducted in 12 healthy young adults.

These results support the notion that working memory and attention are organised in partly overlapping neural circuits. In contrast to previous reports in the visual or auditory domain, this study emphasises the involvement of the anterior insula in vibrotactile working memory and selective attention.

Faced with a continuous stream of afferent data, somatosensory processing requires not only the analysis of the properties of tactile stimuli, but also the extraction and encoding of novel, relevant information [1]. The integration of tactile information retrieved from cutaneous afferents, traditionally attributed to the primary (SI) and secondary somatosensory cortices (SII), has been extensively studied [2]. In contrast, the neural basis of tactile working memory and tactile selective attention is less well known.

These higher-level cognitive processes are nevertheless crucial for managing many challenges of every-day life. Pulling out a key from a coat pocket in the dark requires, amongst others, exploratory finger movements, attention to tactile information derived from the exploring hand (and not, e.g., from the other hand holding a bag), storage of this information in working memory, and integration of the successively obtained tactile information. Studies on patients with focal lesions suggest that the prefrontal cortex [3,4], right parietal cortex[5] and thalamus [6] are involved in the inhibition of task-irrelevant tactile information. Lesions of the medial temporal lobe, in contrast, have been shown to impair tactile working memory in patients [7].

Brain activation associated with processing of the probe. The figure shows brain activation and deactivation associated with the processing of the probe (either 25 Hz or higher) across all conditions (clustered activation images with an overall corrected p < 0.05). Activated areas are colour-coded in yellow and red, deactivated areas are displayed in blue. Activation is seen in the left cerebellar hemisphere (1), the bilateral anterior insula (2, 3), the bilateral head of the caudate nucleus and the globus pallidus (4, 5), the bilateral thalamus (6, 7), the right inferior frontal cortex (8), the anterior cingulate cortex (9), the left (contralateral) sensorimotor cortex (10), the right posterior parietal cortex (11) and the supplementary motor area (12). Deactivation was found in the right parahippocampal gyrus (13), the bilateral medial frontal gyrus (14), the right cuneus (15), the bilateral posterior cingulate gyrus (16), the bilateral precuneus (16) and the left superior frontal gyrus (17). Brain images are shown in radiological convention (the right hemisphere is seen on the left side of the image).

The results of the present study demonstrate that vibrotactile frequency discrimination is associated with the activation of distributed neural networks, in particular the central somatosensory pathways, the motor system, and the polymodal frontal, parietal and insular cortices (Fig. 1).

The chosen vibrotactile stimuli with a frequency around 25 Hz activate primarily Meissner’s corpuscles, located in the dermal-epidermal junction of the superficial glabrous skin [10].

Based on these reports, it is hypothesised that the bilateral anterior insula is involved in the analysis of the temporal aspects of vibrotactile stimuli. In support of this hypothesis, passive vibrotactile stimulation without discrimination between stimuli of different frequency [1318,30] did not activate the anterior insula.

Compared with baseline, vibrotactile frequency discrimination was associated with deactivation in the frontal cortex (medial and superior frontal gyrus), the cuneus, the precuneus, the parahippocampal area and the posterior cingulate gyrus (Fig 3). These areas probably reflect a widespread neuronal network that is consistently activated during rest or during less demanding tasks, termed the default mode network [31].

The present study demonstrates that vibrotactile frequency discrimination is associated with the activation of distributed neural circuits including the somatomotor system, and polymodal frontal, parietal, and insular areas.

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