Hemispatial neglect that improves and hemispatial neglect that does not?
Hemispatial neglect and networks
One symptom relating to stroke that is frequently seen in a clinical setting is hemispatial neglect.
In most cases of hemispatial neglect, a phenomenon occurs where attention to the left side declines and the patient has difficulty noticing things on the left side when walking or eating, for instance.
When observing a patient’s progress after developing symptoms of hemispatial neglect, there are some symptoms that improve and others that do not. What kind of neurological mechanism is related to this?
The paper I discuss today investigates the brain activity of patients exhibiting symptoms of hemispatial neglect over time.
The hemispatial neglect symptom of ignoring the left side can be broadly divided into two mechanisms.
One is that attention is directed excessively towards the right side, resulting in neglect of the left side, and the other is the inability to switch attention to the left side.
As shown in the diagram above, activity in the right hemisphere decreases while activity in the left hemisphere increases as if to compensate and restore balance, leading to excessive attention to the right side, while in the other, if the region relating to attention switching (moving the focus of attention to something else) is not operating properly, switching attention from the right side to the left will become difficult.
In other words, if attention is directed solely to the right side and this is difficult to correct (difficulty in switching), these could be a symptom of hemispatial neglect.
In this study, researchers used functional MRI to investigate the brain activity of 11 patients (average age: 60 years; 8 females) who exhibited left hemispatial neglect due to injury in the right frontoparietal region, in the period early after expressing symptoms (3–4 weeks) and in the chronic period (6 months or longer). The study showed that even without injury to the parietal regions involved in attention switching, injury to the ventral parietal regions that connect to them causes secondary decreases in activity in the parietal and occipital regions, resulting in the appearance of hemispatial neglect symptoms, and that in cases of recovery, activity in these regions that were structurally uninjured to begin with recovers and the hemispatial neglect symptoms improve.
A derailment in one train line can disrupt the operation of other train lines, and I wondered if the same sort of thing might be happening in the brain.
Reference URL: Neural basis and recovery of spatial attention deficits in spatial neglect.
[Abstract]
The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex. This syndrome shows spontaneous partial recovery, but the neural basis of both spatial neglect and its recovery is largely unknown. We show that spatial attention deficits in neglect (rightward bias and reorienting) after right frontal damage correlate with abnormal activation of structurally intact dorsal and ventral parietal regions that mediate related attentional operations in the normal brain. Furthermore, recovery of these attention deficits correlates with the restoration and rebalancing of activity within these regions. These results support a model of recovery based on the re-weighting of activity within a distributed neuronal architecture, and they show that behavioral deficits depend not only on structural changes at the locus of injury, but also on physiological changes in distant but functionally related brain areas.
