Gait impairment during complex walking in older adults is thought to result from a progressive failure to compensate for deteriorating peripheral inputs by central neural processes. It is the primary hypothesis of this paper that failure of higher cerebral adaptations may already be present in middle-aged adults who do not present observable gait impairments. We therefore compared metabolic brain activity during steering of gait (i.e., complex locomotion) and straight walking (i.e., simple locomotion) in young and middle-aged individuals. Cerebral distribution of [18F]-fluorodeoxyglucose, a marker of brain synaptic activity, was assessed during over ground straight walking and steering of gait using positron emission tomography in seven young adults (aged 24±3) and seven middle-aged adults (aged 59±3). Brain regions involved in steering of gait (posterior parietal cortex, superior frontal gyrus, and cerebellum) are retained in middle-age. However, despite similar walking performance, there are age-related differences in the distribution of [ 18F]-FDG during steering: middle-aged adults have (i) increased activation of precentral and fusiform gyri, (ii) reduced deactivation of multisensory cortices (inferior frontal, postcentral, fusiform gyri), and (iii) reduced activation of the middle frontal gyrus and cuneus. Our results suggest that pre-clinical decline in central sensorimotor processing in middle-age is observable during complex walking.
Crossed cerebellar diaschisis (CCD) is well described in the chronic phase of stroke, but few data describe acute CCD and its serial changes after reperfusion. Using positron emission tomography (PET), we studied acute CCD with respect to supratentorial perfusion and outcome measures. In 19 acute stroke patients receiving intravenous thrombolysis (<3 h), 15O-water PET assessed CCD and supratentorial hypoperfusion volume before thrombolysis, 3, 24 h and 14 days later. Infarct volume at day 14 and NIHSS score at 3 months were assessed. Supratentorial hypoperfusion decreased from 25 cm3 (median) before thrombolysis to 0.1 cm3 at day 14. Baseline CCD was 13.4% and decreased continuously to 6.1% after 14 days. The NIHSS score decreased from 11 to 4 pts after 3 months. Infarct volume was 1.1 cm3. Crossed cerebellar diaschisis correlated to the hypoperfusion volume within the first 24 h after stroke, but not later. Hypoperfusion correlated to outcome measures at the early stage only. In contrast, CCD correlated to outcome values at all four measurements. Reperfusion with recovery of CCD was seen in patients with small infarcts and good clinical outcome and vice versa. Our data suggest that (i) CCD occurs as early as 3 h after stroke and might be reversible; (ii) acute CCD is closely related to the volume of supratentorial hypoperfusion. At later time points, however, CCD is disconnected from supratentorial perfusion but strongly associated to outcome measures; (iii) CCD is not susceptible to non-nutritional reperfusion and adds valuable information to interpret supratentorial reperfusion patterns.
This study was designed to determine patterns of regional brain activation during emotional stimulation in alexithymics as compared with normal controls. We used 15O-water positron emission tomography and an emotional stimulation paradigm based upon autobiographic recall of either happy, sad or emotionally neutral situations. 10 normal subjects without medical or psychiatrical history were compared with 9 patients with somatoform disorder without any other DSM-IV diagnosis. TAS-20 was used as a measure for alexithymia, depression was measured using BDI. Normal controls showed significantly greater activation than alexithymics in cingulate areas, corpus callosum, and right superior and inferior frontal gyrus. Alexithymics activated significantly more in cuneus and precuneus, thalamus (pulvinar), left medial frontal, right inferior temporal, left superior temporal regions, left precentral gyrus, and the cerebellum. During emotional autobiographic recall, alexithymia, either trait or state, is characterized by utilization of different brain regions when compared to normal controls. The areas activated by alexithymic persons largely comprise of language related regions, leaving out limbic and paralimbic areas.
What distinguishes the recall of real-life experiences from that of self-created, fictitious emotionally laden information? Both kinds of information belong to the episodic memory system. Autobiographic memories constitute that part of the episodic memory system that is composed of significant life episodes, primarily of the distant past. Functional imaging was used to study the neural networks engaged in retrieving autobiographic and fictitious information of closely similar content. The principally activated brain regions overlapped considerably and constituted temporal and inferior prefrontal regions plus the cerebellum. Selective activations of the right amygdala and the right ventral prefrontal cortex (at the level of the uncinate fascicle interconnnecting prefrontal and temporopolar areas) were found when subtracting fictitious from autobiographic retrieval. Furthermore, distinct foci in the left temporal lobe were engaged. These data demonstrate that autobiographic memory retrieval uses (at least in non-brain damaged individuals) a network of right hemispheric ventral prefrontal and temporopolar regions and left hemispheric lateral temporal regions. It is concluded that it is the experiential character, its special emotional infiltration and its arousal which distinguishes memory of real-life from that of fictitious episodes. Consequently, our results point to the engagement of a bi-hemispheric network in which the right temporo-prefrontal hemisphere is likely to be responsible for the affective/arousal side of information retrieval and the left-hemispheric temporal gyrus for its engram-like representation. Portions of the neural activation found during retrieval might, however, reflect re-encoding processes as well.