Neural Substrates for Head Movements in Humans: A Functional Magnetic Resonance Imaging Study.

The neural systems controlling head movements are not well delineated in humans. It is not clear whether the ipsilateral or contralateral primary motor cortex is involved in turning the head right or left. Furthermore, the exact location of the neck motor area in the somatotopic organization of the motor homunculus is still debated and evidence for contributions from other brain regions in humans is scarce. Because currently available neuroimaging methods are not generally suitable for mapping brain activation patterns during head movements, we conducted fMRI scans during isometric tasks of the head. During isometric tasks, muscle contractions occur without an actual movement and they have been used to delineate patterns of brain activity related to movements of other body parts such as the hands. Healthy individuals were scanned during isometric head rotation or wrist extension. Isometric wrist extension was examined as a positive control and to establish the relative locations of head and hand regions in the motor cortex. Electromyographic recordings of neck and hand muscles during scanning ensured compliance with the tasks. Increased brain activity during isometric head rotation was observed bilaterally in the precentral gyrus, both medial and lateral to the hand area, as well the supplementary motor area, insula, putamen, and cerebellum. These findings clarify the location of the neck region in the motor homunculus and help to reconcile some of the conflicting results obtained in earlier studies.

Mnemonic strategy training improves memory for object location associations in both healthy elderly and patients with amnestic mild cognitive impairment: a randomized, single-blind study.

OBJECTIVE: To evaluate the efficacy of mnemonic strategy training versus a matched-exposure control condition and to examine the relationship between training-related gains, neuropsychological abilities, and medial temporal lobe volumetrics in patients with amnestic mild cognitive impairment (aMCI) and age-matched healthy controls. METHOD: Twenty-three of 45 screened healthy controls and 29 of 42 screened patients with aMCI were randomized to mnemonic strategy or matched-exposure groups. Groups were run in parallel, with participants blind to the other intervention. All participants completed five sessions within 2 weeks. Memory testing for object-location associations (OLAs) was performed during sessions one and five and at a 1-month follow-up. During Sessions 2-4, participants received either mnemonic strategy training or a matched number of exposures with corrective feedback for a total of 45 OLAs. Structural magnetic resonance imaging was performed in most participants, and medial temporal lobe volumetrics were acquired. RESULTS: Twenty-one healthy controls and 28 patients with aMCI were included in data analysis. Mnemonic strategy training was significantly more beneficial than matched exposure immediately after training, p = .006, partial η2 = .16, and at 1 month, p < .001, partial η2 = .35, regardless of diagnostic group (healthy group or aMCI group). Although patients with aMCI demonstrated gains comparable to the healthy control groups, their overall performance generally remained reduced. Mnemonic strategy-related improvement was correlated positively with baseline memory and executive functioning and negatively with inferior lateral ventricle volume in patients with aMCI; no significant relationships were evident in matched-exposure patients. CONCLUSION: Mnemonic strategies effectively improve memory for specific content for at least 1 month in patients with aMCI.

Tactile co-activation improves detection of afferent spatial modulation.

Tactile co-activation, i.e., synchronous stimulation of a region of skin, has been reported to improve tactile spatial acuity and expand the corresponding somatosensory cortical representation. The current study aimed to clarify the nature of the changes resulting from tactile co-activation, using three measures of tactile sensitivity obtained with controlled mechanical stimulation. One was the grating orientation (GR/OR) discrimination task, where acuity is indexed by the threshold groove width required for 75% correct discrimination between two orthogonal orientations of a grating on the fingerpad. Since this task may be susceptible to intensity cues due to tactile anisotropy, another acuity measure, the 3-dot task, was also used. In this task, the acuity threshold corresponds to 75% correct discrimination of the direction of offset of the central dot in a 3-dot array. In Experiment 1, co-activation failed to induce significant improvement in acuity with either of these measures. Experiment 2 employed both the GR/OR task, and a third measure based on discriminating a grooved from a smooth surface (SM/GV). While the former task demands detailed spatial resolution, the latter requires only that spatial modulation in the afferent population be detected. This experiment also included a control group. GR/OR performance did not significantly improve for either the control or experimental groups. There was, however, a significant improvement in SM/GV performance following co-activation for the experimental but not the control group. These findings indicate that the SM/GV task may be better suited than the GR/OR or 3-dot tasks for measuring changes in tactile sensitivity following co-activation.