Page "Persistent vegetative state" Paragraph 41

Also, there is evidence of partially functional cerebral regions in catastrophically injured brains.

To study five patients in PVS with different behavioral features, researchers employed PET, MRI and magnetoencephalographic ( MEG ) responses to sensory stimulation.

In three of the five patients, co-registered PET / MRI correlate areas of relatively preserved brain metabolism with isolated fragments of behavior.

Two patients had suffered anoxic injuries and demonstrated marked decreases in overall cerebral metabolism to 30 – 40 % of normal.

Two other patients with non-anoxic, multifocal brain injuries demonstrated several isolated brain regions with higher metabolic rates, that ranged up to 50 – 80 % of normal.

Nevertheless, their global metabolic rates remained < 50 % of normal.

MEG recordings from three PVS patients provide clear evidence for the absence, abnormality or reduction of evoked responses.

Despite major abnormalities, however, these data also provide evidence for localized residual activity at the cortical level.

Each patient partially preserved restricted sensory representations, as evidenced by slow evoked magnetic fields and gamma band activity.

In two patients, these activations correlate with isolated behavioral patterns and metabolic activity.

Remaining active regions identified in the three PVS patients with behavioral fragments appear to consist of segregated corticothalamic networks that retain connectivity and partial functional integrity.

A single patient who suffered severe injury to the tegmental mesencephalon and paramedian thalamus showed widely preserved cortical metabolism, and a global average metabolic rate of 65 % of normal.

The relatively high preservation of cortical metabolism in this patient defines the first functional correlate of clinical – pathological reports associating permanent unconsciousness with structural damage to these regions.

The specific patterns of preserved metabolic activity identified in these patients reflect novel evidence of the modular nature of individual functional networks that underlie conscious brain function.

The variations in cerebral metabolism in chronic PVS patients indicate that some cerebral regions can retain partial function in catastrophically injured brains ( Schiff et al., 2002 ).