Brain responses during the first desire to void: a positron emission tomography study

Functional brain networks associated with the urge for action: Implications for pathological urge

Tics in Tourette syndrome (TS) are often preceded by sensory urges that drive the motor and vocal symptoms. Many everyday physiological behaviors are associated with sensory phenomena experienced as an urge for action, which may provide insight into the neural correlates of this pathological urge to tic that remains elusive. This study aimed to identify a brain network common to distinct physiological behaviors in healthy individuals, and in turn, examine whether this network converges with a network we previously localized in TS, using novel 'coordinate network mapping' methods. Systematic searches were conducted to identify functional neuroimaging studies reporting correlates of the urge to micturate, swallow, blink, or cough. Using activation likelihood estimation meta-analysis, we identified an 'urge network' common to these physiological behaviors, involving the bilateral insula/claustrum/inferior frontal gyrus/supplementary motor area, mid-/anterior- cingulate cortex (ACC), right postcentral gyrus, and left thalamus/precentral gyrus. Similarity between the urge and TS networks was identified in the bilateral insula, ACC, and left thalamus/claustrum. The potential role of the insula/ACC as nodes in the network for bodily representations of the urge to tic are discussed.

Baseline Brain Segmental Volumes in Responders and Nonresponders to Anticholinergic Therapy for Overactive Bladder Syndrome

OBJECTIVE

Evaluate structural differences in brains of responders (R) and nonresponders (NR) to anticholinergic (AC) therapy for overactive bladder (OAB).

MATERIALS AND METHODS

This was a retrospective cohort study of age matched women treated with an AC medication for OAB and underwent magnetic resonance imaging within 12 months before treatment. Data on pretreatment demographic and clinical variables and symptom severity was also collected.T1-weighted magnetic resonance images of the brain for each subject were segmented using FreeSurfer software. Structures included for analysis were cerebral cortex, white matter, subcortical gray matter, cerebellum, and brain stem.Nonresponders were defined as patients who reported less than 50% improvement after a minimum of 4 weeks on the maximum dose of the prescribed medication. Pairwise analysis between groups was performed using the Wilcoxon-Rank Sum test and Fisher exact test where appropriate. Spearman ρ was used to evaluate for correlations between neurologic structures and symptom severity.

RESULTS

There were no differences in pretreatment characteristics or symptom severity between the 21 R and 18 NR. Nonresponders had lower volumes of the right caudal anterior cingulate gyrus white matter (1919 mm3 vs 2416 mm3, P = 0.008) and right parahippocampal gyrus white matter (1008 mm3 vs 1469 mm3, P = 0.001). Incontinence episode frequency showed a negative moderate correlation with the anterior cingulate gyrus white matter volume (ρ = -0.4228, P = 0.007). The right and left cerebellar cortices showed weak and moderate negative correlations to frequency of nocturia (ρ = -0.384, P = 0.02 and ρ -0.443, P = 0.005, respectively).

CONCLUSION

There are measurable volumetric differences in brain structures in R and NR to AC therapy.

[A case of oculomotor disorder and urinary retention due to a lower midbrain lesion]

We report an 86-year-old woman who suffered sudden onset of diplopia while cooking. The patient presented with binocular diplopia, bilateral adduction weakness, convergence disorder and bilateral abduction nystagmus. Although brain MRI on admission detected no abnormality, a repeat MRI examination on the following day demonstrated a focal hyperintense lesion in the tegmentum of the midbrain on diffusion-weighted images. At 36 hours after admission, lower abdominal distension became apparent, and about 1 liter of urine was drained via a urethral catheter. Bladder filling sensation was not present, and we considered that the midbrain lesion had been responsible for the oculomotor disorder and urinary retention. As cerebral infarction was the most likely pathology of this lesion, an antiplatelet agent was administered. At two months after onset, the eye movement disorder was resolved and there was no diplopia. Bladder voiding also resumed at normal intervals. We considered that the bilateral medial longitudinal fasciculi and subgroups of the oculomotor nucleus, which contain motor neurons supplying the medial rectus muscle, had been responsible for the oculomotor disorder. The urinary retention was thought to have been caused by a lesion in the periaqueductal gray, which is one structure controlling micturition. This was a rare case of urinary retention due to a small midbrain infarction.

Cerebellum and micturition: what do we know? A systematic review

Aims

Micturition depends on a complex voluntary and involuntarily neuronal network located at various levels of the nervous system. The mechanism is highly dependent on the hierarchical organization of central nervous system pathways. If the role of the cortex and brainstem centres is well established, the role of other subcortical areas structures, such as the cerebellum is poorly understood. We are interested in discussing the current knowledge on the role of cerebellum in micturition.

Methods

A systematic search is performed in the medical literature, using the PubMed database with the keyword « cerebellum ». The latter is combined with «urination » OR « micturition » OR « urinary bladder ».

Results

Thirty-one articles were selected, focussing on micturition and describing the role of the cerebellum. They were grouped in 6 animal experimental studies, 20 functional brain imaging in micturition and 5 clinical studies.

Conclusions

Although very heterogeneous, experimental and clinical data clearly indicate the cerebellum role in the micturition control. Cerebellum modulates the micturition reflex and participates to the bladder sensory-motor information processing. The cerebellum is involved in the reflex micturition modulation through direct or indirect pathways to major brainstem or forebrain centres.

Regions of the brain activated in bladder filling vs rectal distention in healthy adults: A meta-analysis of neuroimaging studies

AIMS

Adults with pelvic floor disorders commonly present with overlapping bladder and bowel symptoms; however, the relationship between urinary and defecatory dysfunction is not well understood. Our aim was to compare and determine if overlapping brain regions are activated during bladder filling and rectal distention in healthy adults.

METHODS

We conducted separate Pubmed searches for neuroimaging studies investigating the effects of rectal distention and bladder filling on brain activation in healthy subjects. Coordinates of activated regions were extracted with cluster-level threshold P < .05 and compared using the activation likelihood estimate approach. Results from the various studies were pooled and a contrast analysis was performed to identify any common areas of activation between bladder filling and rectal distension.

RESULTS

We identified 96 foci of activation from 14 neuroimaging studies on bladder filling and 182 foci from 17 studies on rectal distension in healthy adults. Regions activated during bladder filling included right insula, right and left thalamus, and right periaqueductal grey. Regions activated during rectal distention included right and left insula, right and left thalamus, left postcentral gyrus, and right inferior parietal lobule. Contrast analysis revealed common activation of the right insula with both rectal distention and bladder filling.

CONCLUSION

Bladder filling and rectal distention activate several separate areas of the brain involved in sensory processing in healthy adults. The common activation of the insula, the region responsible for interoception, in these two conditions may offer an explanation for the coexistence of bladder and defecatory symptoms in pelvic floor disorders.

The Role of the Periaqueductal Gray Matter in Lower Urinary Tract Function

The periaqueductal gray matter (PAG), as one of the mostly preserved evolutionary components of the brain, is an axial structure modulating various important functions of the organism, including autonomic, behavioral, pain, and micturition control. It has a critical role in urinary bladder physiology, with respect to storage and voiding of urine. The PAG has a columnar composition and has extensive connections with its cranially and caudally located components of the central nervous system (CNS). The PAG serves as the control tower of the detrusor and sphincter contractions. It serves as a bridge between the evolutionary higher decision-making brain centers and the lower centers responsible for reflexive micturition. Glutamatergic cells are the main operational neurons in the vlPAG, responsible for the reception and relay of the signals emerging from the bladder, to related brain centers. Functional imaging studies made it possible to clarify the activity of the PAG in voiding and filling phases of micturition, and its connections with various brain centers in living humans. The PAG may be affected in a wide spectrum of disorders, including multiple sclerosis (MS), migraine, stroke, Wernicke’s encephalopathy, and idiopathic normal pressure hydrocephalus, all of which may have voiding dysfunction or incontinence, in certain stages of the disease. This emphasizes the importance of this structure for the basic understanding of voiding and storage disorders and makes it a potential candidate for diagnostic and therapeutic interventions.

Brain activation in response to bladder filling in healthy adults: An activation likelihood estimation meta-analysis of neuroimaging studies

AIMS

Recent studies have used different neuroimaging techniques and identified various brain regions that are activated during bladder filling. However, there is a lack of consensus regarding which of these brain regions regulate the process of urine storage. The aim of this meta-analysis is to identify brain regions that are commonly activated during bladder filling in healthy adults across different studies.

METHODS

PubMed was searched for neuroimaging studies investigating the effects of bladder filling on regional brain activation. Studies were excluded if they did not report brain activation differences from whole-brain group analysis by comparing the state of bladder filling with the state of bladder rest. The current version of the activation likelihood estimation (ALE) approach was used for meta-analysis.

RESULTS

We identified 14 neuroimaging studies examining brain activation in response to experimental bladder filling in 181 healthy subjects, which reported 89 foci for ALE analysis. The meta-analysis revealed significant activation in multiple brain regions including thalamus (bilaterally), right insula, cerebellum, and brainstem (bilaterally).

CONCLUSIONS

Several key brain regions involved in sensory processing are commonly activated during bladder filling in healthy adults across different studies. Neurourol. Urodynam. 36:960-965, 2017. © 2016 Wiley Periodicals, Inc.

Anatomy and physiology of the lower urinary tract

Functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. Neural control of micturition is organized as a hierarchic system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brainstem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brainstem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily during the early postnatal period, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults cause re-emergence of involuntary micturition, leading to urinary incontinence. The mechanisms underlying these pathologic changes are discussed.

Neural control of the lower urinary tract

This article summarizes anatomical, neurophysiological, pharmacological, and brain imaging studies in humans and animals that have provided insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract. The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. The neural control of micturition is organized as a hierarchical system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brain stem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brain stem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary micturition, leading to urinary incontinence. Neuroplasticity underlying these developmental and pathological changes in voiding function is discussed.

Neuroimaging of the periaqueductal gray: state of the field

This review and meta-analysis aims at summarizing and integrating the human neuroimaging studies that report periaqueductal gray (PAG) involvement; 250 original manuscripts on human neuroimaging of the PAG were identified. A narrative review and meta-analysis using activation likelihood estimates is included. Behaviors covered include pain and pain modulation, anxiety, bladder and bowel function and autonomic regulation. Methods include structural and functional magnetic resonance imaging, functional connectivity measures, diffusion weighted imaging and positron emission tomography. Human neuroimaging studies in healthy and clinical populations largely confirm the animal literature indicating that the PAG is involved in homeostatic regulation of salient functions such as pain, anxiety and autonomic function. Methodological concerns in the current literature, including resolution constraints, imaging artifacts and imprecise neuroanatomical labeling are discussed, and future directions are proposed. A general conclusion is that PAG neuroimaging is a field with enormous potential to translate animal data onto human behaviors, but with some growing pains that can and need to be addressed in order to add to our understanding of the neurobiology of this key region.