Increased amygdala reactivity following early life stress: a potential resilience enhancer role.

BACKGROUND: Amygdala hyper-reactivity is sometimes assumed to be a vulnerability factor that predates depression; however, in healthy people, who experience early life stress but do not become depressed, it may represent a resilience mechanism. We aimed to test these hypothesis examining whether increased amygdala activity in association with a history of early life stress (ELS) was negatively or positively associated with depressive symptoms and impact of negative life event stress in never-depressed adults. METHODS: Twenty-four healthy participants completed an individually tailored negative mood induction task during functional magnetic resonance imaging (fMRI) assessment along with evaluation of ELS. RESULTS: Mood change and amygdala reactivity were increased in never-depressed participants who reported ELS compared to participants who reported no ELS. Yet, increased amygdala reactivity lowered effects of ELS on depressive symptoms and negative life events stress. Amygdala reactivity also had positive functional connectivity with the bilateral DLPFC, motor cortex and striatum in people with ELS during sad memory recall. CONCLUSIONS: Increased amygdala activity in those with ELS was associated with decreased symptoms and increased neural features, consistent with emotion regulation, suggesting that preservation of robust amygdala reactions may reflect a stress buffering or resilience enhancing factor against depression and negative stressful events.

The evaluation of oral health in stroke patients.

OBJECTIVE: As tooth loss has been suggested as a potential risk factor for stroke, oral examinations were carried out on stroke patients to review the oral condition of those patients. METHOD: The subjects were patients consecutively discharged from the recovery rehabilitation unit of Hiroshima City General Rehabilitation Center between April 2008 and December 2009. All patients were offered oral examination and 358 of 443 patients accepted. Patients receiving dental examination were divided into two groups: one group comprising stroke patients and the second, patients with other disorders. These two groups were then compared for the number of remaining teeth by age group. RESULTS: Among the examined patients, the number of remaining teeth in stroke patients in their 50s and 60s was significantly lower than for patients in corresponding age groups (18.4 ± 9.4 vs. 24.5 ± 5.4 and 18.3 ± 9.2 vs. 22.2 ± 7.2, respectively, with p < 0.05 for both age groups) who were hospitalised for other conditions. In addition, the number of remaining teeth in stroke patients in their 50s was also significantly lower than the number reported in the Survey of Dental Diseases (24.1 ± 6.1; p < 0.05). CONCLUSION: The results of this study suggest an association between tooth loss and early occurrence of stroke.

[Management of secondary normal pressure hydrocephalus and assessment of cortical reorganization using fMRI].

We assessed the motor recovery and cortical reorganization associated with intracranial pressure (ICP) control in a secondary normal pressure hydrocephalus (sNPH) patient. A 32-year-old man with sNPH resulting from a head injury presented with left hemiplegia. A ventricular-peritoneum shunt (VP shunt) was surgically inserted for the sNPH using a Codman Hakim Programmable Valve, and his ICP was controlled according to the ventricular size by CT scanning. The motor function of the patient was evaluated by functional MRI (fMRI) during ICP control in our hospital. The fMRI was performed at 3.0 T with timed dorsal flexion-extension movement of the foot. After 3 months of shunt valve pressure control, the primary sensorimotor cortex (SM1) was activated during the affected (left) foot movement, an area that had not been able to be activated just after admission. His walking ability also recovered markedly to the point of free independent walking. The motor function of the affected lower extremity appeared to recover to almost the some degree the original motor area after control of the ICP. This finding may reflect functional reorganization of the motor pathway following ICP normalization.

Further evidence for excitability changes in human primary motor cortex during ipsilateral voluntary contractions.

The present study aimed to further investigate whether the intracortical neural circuits within the primary motor cortex (M1) are modulated during ipsilateral voluntary finger movements. Single- and paired-pulse (interstimulus intervals, ISIs; 3 ms and 12 ms) transcranial magnetic stimulations of the left M1 were applied to elicit motor evoked potential (MEP) in the right first dorsal interosseous (Rt-FDI) muscle during voluntary contractions (10% and 30% maximum voluntary contraction) of the left FDI (Lt-FDI) muscle. F-waves of Rt-FDI muscle were recorded under these left index-finger conditions for ensuring that the excitability changes occur at the supraspinal level. MEPs were also recorded during motor imagery of the left index-finger abduction instead of overt movement. The results showed that, in single-pulse transcranial magnetic stimulation (TMS) paradigm, MEPs in Rt-FDI muscle were markedly enhanced during voluntary contractions of Lt-FDI muscle compared with the complete resting state. In paired-pulse TMS paradigm, the short intracortical inhibition was significantly reduced in proportion to increments of the ipsilateral muscle contraction, whereas the intracortical facilitation had no change. F-wave of Rt-FDI muscle was unchanged under these conditions, while MEP in Rt-FDI muscle was also enhanced during motor imagery of the left index-finger abduction. Based on the present results, it is suggested that the intracortical inhibitory neural circuits may be modulated in the transition from rest to activity of the ipsilateral homonymous muscle. The excitability changes in M1 might be induced by overflows of voluntary drive given to the ipsilateral limb, probably via the transcallosal pathway.

Temporal modulations of agonist and antagonist muscle activities accompanying improved performance of ballistic movements.

Although many studies have examined performance improvements of ballistic movement through practice, it is still unclear how performance advances while maintaining maximum velocity, and how the accompanying triphasic electromyographic (EMG) activity is modified. The present study focused on the changes in triphasic EMG activity, i.e., the first agonist burst (AG1), the second agonist burst (AG2), and the antagonist burst (ANT), that accompanied decreases in movement time and error. Twelve healthy volunteers performed 100 ballistic wrist flexion movements in ten 10-trial sessions under the instruction to "maintain maximum velocity throughout the experiment and to stop the limb at the target as fast and accurately as possible". Kinematic parameters (position and velocity) and triphasic EMG activities from the agonist (flexor carpi radialis) and antagonist (extensor carpi radialis) muscles were recorded. Comparison of the results obtained from the first and the last 10 trials, revealed that movement time, movement error, and variability of amplitudes reduced with practice, and that maximum velocity and time to maximum velocity remained constant. EMG activities showed that AG1 and AG2 durations were reduced, whereas ANT duration did not change. Additionally, ANT and AG2 latencies were reduced. Integrated EMG of AG1 was significantly reduced as well. Analysis of the alpha angle (an index of the rate of recruitment of the motoneurons) showed that there was no change in either AG1 or AG2. Correlation analysis of alpha angles between these two bursts further revealed that the close relationship of AG1 and AG2 was kept constant through practice. These findings led to the conclusion that performance improvement in ballistic movement is mainly due to the temporal modulations of agonist and antagonist muscle activities when maximum velocity is kept constant. Presumably, a specific strategy is consistently applied during practice.

Effects of motor imagery are dependent on motor strategies.

To investigate whether the facilitatory effects of motor imagery (MI) are dependent on motor strategies that vary with posture, we used transcranial magnetic stimulation to examine the effects of two forearm positions on motor-evoked potentials during an MI of index-finger abduction. MI-enhanced motor-evoked potentials of the first dorsal interosseous (prime mover) muscle in the forearm prone position were larger than those in the forearm neutral position. The opposite effects were seen in the extensor carpi radialis (synergist) muscle. These effects correspond to the different electromyography activities in the muscles when performing the actual movements in these two forearm positions. It is suggested that MI reflects different motor strategies in the contribution of agonist and synergist muscles towards a motor task.

Decreased cortical excitability during motor imagery after disuse of an upper limb in humans.

OBJECTIVE: The present study investigated the effect of joint immobilization on corticomotoneuronal excitability to only intracortical input from a hierarchical level above the primary motor cortex. METHODS: Motor evoked potentials (MEPs) and H-reflexes in the flexor carpi radialis muscle were elicited from 8 orthopedic patients with splints and 8 healthy volunteers. Each patient was examined on the day of splint removal (disuse stage) and 2 months after that day (recovery stage). Both potentials were recorded under 3 conditions: at rest, while imagining motor movement (during motor imagery), and during 10% of maximum voluntary contraction (10% MVC). RESULTS: In the patient group, the amplitude of surface electromyography during voluntary maximum wrist flexion was lower at the disuse stage than at the recovery stage, although the supra-maximum M-wave amplitude did not change between stages. Compared to both the patient group at the recovery stage and the control group, patients at the disuse stage recorded significantly lower MEPs, but only during motor imagery. In contrast, the H-reflex amplitudes were not significantly changed under any of the 3 conditions for both patients and control. CONCLUSIONS: The present results indicated a strict parallelism between motor execution (the reduction of electromyography during mvc after immobilization) and motor imagery (the reduction of MEP-amps after immobilization). This parallelism suggests that a functional reorganization or decreased excitability in the cerebral cortex area involved in executing movement likely decreases the motor capability to produce voluntary muscular output after immobilization.