Neurocase (2002) Vol. 8, pp. 323–329 © Oxford University Press 2002 Visuospatial Hemi-inattention Following Cerebellar/Brain Stem Bleeding H. Hildebrandt1,3, K. Spang2 and M. Ebke1 1Department of Neurology, Central Hospital Bremen-Ost, Züricher Str. 40, 28325 Bremen, 2Institute for Neurobiology, University of Bremen, 28211 Bremen and 3Department of Psychology, University of Oldenburg, 26111 Oldenburg, Germany Abstract Neglect is a unilateral lack of responsiveness to stimuli caused by visuospatial hemi-inattention, a unilateral representation deficit and/or a unilateral hypokinesia. It results most frequently from right-hemisphere brain damage, particularly of the parietal lobe but also of the frontal cortex, the basal ganglia, the thalamus, and recently it has also been described after a cerebellar lesion. We report a patient with right-sided bleeding of the posterior inferior cerebellar artery, who developed a left-sided visual hemi-inattention. She had no visual field defects, yet she had problems detecting left-sided targets in visual extinction. Furthermore, she was impaired in detecting complex motion on the left side and targets in a fixation offset paradigm. Reactions to left-sided targets in covert shifts of attention were slowed in the invalid condition. Her text reading was impaired as she could not always find the initial word of the next line. However, she was aware of her deficit. Her visuoconstructive ability was normal and she gave no indication of tactile or acoustic extinction. As the cerebellar lesion was located in the right hemisphere and the inattention involved the left side of space, we suggest that the damage to the right brain stem led to a transient imbalance of the noradrenergic ascending activation system which may explain her hemi-inattention. Introduction Neglect is a clinical syndrome which can be defined as a lack of responsiveness to stimuli on a particular side of the environmental space not due to a sensory disorder (Halligan and Marshall, 1994). A consistent aspect of neglect is hemiinattention, while further aspects comprise representational deficits and directional hypokinesia (Bisiach, 1979; Heilman et al., 1987). The neuroanatomical cause for the neglect syndrome is a lesion of a network that includes the right frontal lobe and, particularly, the parietal lobe (Heilman et al., 1987). Neglect following subcortical lesions has recently been reported for thalamic and basal ganglia lesions (Hanlon et al., 1992; Karussis et al., 2000). Leplow and Stunbinger (1994) even found a shift of the subjective horizontal midline after peripheral neurotrauma, and shifts of the subjective vertical midline have regularly been reported after unilateral vestibular brain stem lesions (Dieterich and Brandt, 2000). On the other hand, hemi-inattention due to brain stem lesions has not been described so far, and only one case has been reported with a neglect-like disorder after a cerebellar lesion (Silveri et al., 2001). Theoretically, we can at least assume that such a deficit is possible, as fibre systems, pass along the brain stem, signal via proprioceptive or vestibular feedback the individual physical orientation of the body in relation to the environment. Furthermore, the brain stem is the origin of the (noradrenergic) reticular activating system. Several investigations have shown that both proprioceptive feedback and noradrenergic modulation interact with the cortical visuospatial system (Rubens, 1985; Posner, 1993; Karnath, 1994; Robertson et al., 1998). Unilateral lesions of the caudal and posterior part of the cerebellum may result in problems with distinguishing similar objects, if presented for a short time on one side and if the patients are cued to the other side (Akshoomoff and Courchesne, 1992). Several brain imaging studies have shown that the cerebellum becomes activated in saccades (Nobre et al., 2000), and in exogenously (Kim et al., 1999), or endogenously (Nobre et al., 1997; Kim et al., 1999) cued covert shifts of attention. As recently summarized by Schmahmann (2001a), the cerebellum is connected to the posterior parietal and frontal lobes by specific neuroanatomical fibre systems. Cerebellar lesions may therefore lead to cerebellar diaschisis, mimicking cerebral disorders. However, apart from (saccadic) motor programming and time sequencing, the role of the cerebellum in cognitive functions has not been well established (Daum et al., 2001). Although higher-order visuospatial deficits Correspondence to: H. Hildebrandt, Department of Neurology, Central Hospital Bremen-Ost, Züricher Str. 40, 28325 Bremen, Germany. Tel: ⫹49 421 408 1509; Fax: ⫹49 441 798 192954; e-mail: helmut.hildebrandt@uni-oldenburg.de 324 H. Hildebrandt, K. Spang and M. Ebke following cerebellar lesions have been reported by Schmahmann (2001b), this has not always been replicated and was criticized because of the heterogeneity of lesion locations (Justus and Ivry, 2001). So far, verbal working memory seems to be the best candidate for a cognitive function requiring cerebellar structures (Desmond, 2001). The following report concerns a patient who suffered from a ruptured aneurysm of the basilary artery at the exit of the right posterior inferior cerebellar artery (PICA). The bleeding resulted in a lesion of the right caudal and medial cerebellum and the right brain stem. During the following weeks the patient developed visuospatial inattention of the left side that resembled in many respects the clinical syndrome of neglect. Case report Clinical and neuroradiological findings On admittance, the examination of the 56-year-old woman, a teacher, showed a right-sided marked ataxia and dysmetria, a certain lack of body control, a lateropulsion to the right side and dysphonia with dysarthria. The patient was alert, cooperative and responded adequately. The magnetic resonance imaging scan (see Fig. 1), carried out 6 weeks after the incident, revealed a small lesion in the posterior cranial cavity in the white matter of the right basal cerebellar hemisphere. The corresponding right half of the brain stem in the lower section of the pons and below the pons could not be examined because of a clip artefact. Apart from that, the structures of the posterior cranial cavity were normal and did not show any signs of brain pressure or bleeding. Brain structures above the cerebellum and the brain stem were not involved in the bleeding. Acoustically evoked potentials were normal. Visually evoked potentials (checkerboard pattern) showed a somewhat reduced amplitude of the P100 for the left eye compared with the right eye and a prolonged latency on both sides. The P3 (acoustical oddball paradigm) resulted in marginally delayed latencies and an amplitude that was marked more clearly at Fz than at Cz. Neuro-ophthalmology The patient’s best corrected visual acuity was 20/32 on both eyes. The visual fields tested with an automatic perimeter (Oculus: Twinfield 70° survey program) were both normal. Ocular motility could only be tested for pursuit eye movements and not for torsional movements. Fixation was unstable and the patient had difficulties in pursuing the target. These symptoms are typical of cerebellar lesions. Diplopia was experienced only intermittently. In primary gaze the right eye was lower (hypotropia). The left eye had a slight abduction deficit, with nystagmus during leftward gaze; upward-oriented movements, requiring the activity of the superior rectus muscles, were bilaterally impaired. The most likely cause of the vertical divergence of the eyes was a mild non-committant skew deviation, especially as pupil reaction was normal on both sides and there was no ptosis, hence no sign of a general lesion of the third nerve. Skew deviation caused by lesions of the lower pons or medulla can lead to hypotropia of the ipsilateral eye and can mimic a partial third or fourth nerve palsy (Kömpf, 1998). This interpretation of the symptoms is in line with the patient’s lesion location. Motion perception was investigated by means of three differing sets of dot stimuli presented on a computer monitor (Braun et al., 1998). For each kind of motion the subject saw a small square at a 10° distance from a fixation point and moving upwards or downwards. The square was produced by dots which moved preferentially in one direction or were stationary, and it was surrounded by further dots all over the screen that moved in random directions. The subject had to indicate whether the square seemed to move upwards or downwards. Responses were evaluated separately for both hemi-fields. In the first type of motion condition, the dots within the square area moved with the square as if a dotted object moved over a sea of randomly moving dots. In this condition all the dots within the square moved in the same direction, that of the square itself (⫽ Fourier motion). In the second condition, the dots within the square were stationary and only the square moved, again against a background of dots randomly moving in the surrounding area. Note that opposite to Fourier motion, the dots in the square did not move in its direction. Just the area of stationary dots, i.e. the square, moved (⫽ non-Fourier motion). Therefore, elementary motion detectors that signal only the direction of dot motion are unable to detect the square, and thus higher-order detectors are required. In the third condition, the dots within the square moved in the opposite direction to the square itself (⫽ theta motion). In this case the elementary movement detectors signal the opposite direction (cf. Braun et al., 1998). To determine thresholds for motion perception, we varied the percentage of dots within the square following the same direction, and thus the correlation between the moving dots. We started with a correlation of 100% and gradually increased the percentage of dots within the square that moved in random directions. Hence, with 0% correlation the movements of the dots within the square were absolutely identical to the surrounding area and the square was no longer present. Our patient could, without any difficulty, distinguish a simple Fourier movement in both hemi-fields. However, the detection of movement in the left visual field was clearly reduced as soon as the discrimination required higher-order movement detectors (see Table 1), that is, the detection of both kinds of complex movement was impaired in the left, but not in the right visual field (albeit with considerable response variability). Neuropsychological investigation The patient mentioned that her reading was clearly poorer than before the incident. Because of her eye movement disturbance, we suggested using a monocular eye patch. As Visuospatial hemi-inattention 325 Fig. 1. Magnetic resonance imaging T2 slices of the patient taken 6 weeks after the aneurysm clipping. White arrows: right-hemisphere cerebellar bleeding; white stippled arrows: aneurysm clip artefacts. Table 1. Results of the neuro-ophthalmological investigation and the neglect test Patient (left eye only) Motion perceptiona Left visual field Right visual field Fourier motion Non-Fourier motion Theta motion 47.1⫾5.4 ⬎100 74.4⫾6.6 39.7 ⫾2.7 86.35⫾28.8 56.3 ⫾10.0 Neglect test (binocular) Reaction time (ms) Omissions Upper left quadrant 948 8/11 Lower left quadrant 884 4/11 Upper right quadrant 656 2/11 Lower right quadrant 687 0/11 aNumber of elements moving towards the same direction until the movement is detected. this brought about only a partial remission of the complaints, we carried out a full investigation of her visual perception and attention. To determine reading skill, we presented a short text to the subject. Compared with a control group, the patient’s reading was slower (2 min 30 s versus a maximum reading time of 1 min 50 s in the control group) and showed an increased number of errors (eight errors versus a maximum of three errors in the control group). Six of the eight errors occurred when she was trying to find the beginning of the line. In these cases she left out the first word. The other two errors were unsystematic slips of the tongue. She did not ignore the first letter or syllable of a multi-part word, as is known from neglect dyslexia (Robertson and Halligan, 1999). A bisection task with lines 21.5 cm long yielded an average deviation of 2.6 cm towards the ipsilesional side. An agematched control group (n ⫽ 10) erred to the left or right with a standard deviation of 0.32 cm. The filling out of a circle for a clock drawing was carried out successfully. Visuoconstructive performance was investigated with the block design test of the Wechsler Adult Intelligence Scale. The patient reached an age-corrected score of 8, which fell within the range of one standard deviation of the norm group (but may be below her probable pre-morbid performance). Simple visual response time, with and without a warning tone [alertness test of the Attention Test Battery (TAP); Zimmermann and Fimm, 1992], was slowed down: without a warning tone: 341 ms, percentile rank 5; with a warning tone: 390 ms, percentile rank 1. Working memory ability was examined using a ‘two back’ paradigm (Braver et al., 1997; Callicott et al., 1999) in which the subject had to press a button if the digit on the screen was the same as the one before last (TAP, working memory, level III). Her response time (1018 ms, percentile rank 4) was clearly prolonged and an increased number of omissions was observed (eight omissions, percentile rank 1). The neglect test of the TAP was performed to assess visuospatial attention deficits. This test was carried out binocularly in a dimmed room. The subject was seated at a 326 H. Hildebrandt, K. Spang and M. Ebke distance of 50 cm in front of a 17-inch monitor. At this distance, the visual angle extends over 17° to both sides in the horizontal line and over 12° in the vertical line. The subject had to fixate a central square and respond to a flickering stimulus presented among other static stimuli in the periphery. The neglect test allows for a comparison of response times and of the number of omissions for each quadrant of the visual field. Because we found a slowing of visual response times for the alertness test, we only report the omissions and the differences in response times between the left and right hemi-fields. The neglect test showed an inattention to stimuli presented on the left side (see Table 1). Healthy subjects do not neglect any stimuli in this test (Zimmermann and Fimm, 1992). The next step was the Posner paradigm (Posner et al., 1987; covert shift of attention test of the TAP). In this paradigm, the subject was informed, by means of a centrally presented cue (an arrow directed towards the left or right side), about the side expected for the appearance of a target stimulus (a cross presented 8° lateral of a central fixation point). In 80% of the trials, the arrow pointed to the correct direction. However, on the other trials, a false indication was given. Neglect patients are considerably slowed down after invalid cues (Posner et al., 1987), whereas after valid cues their responses may be comparable with those of healthy persons. Our patient showed increased costs after invalid cues to the right. In this condition she needed 41% more time than with valid cues to the left, whereas with targets on the right side she needed only 11% more time after invalid cues. The difference in costs was 16% on the left and 10% on the right side in an age-matched control group (n ⫽ 8) (see Table 2 for raw values). In addition, we investigated saccadic eye movements to a laterally presented stimulus in an ‘overlap’ and a ‘gap’ presentation (eye movements test of the TAP). In the overlap condition there was a permanent stimulus at the centre of the screen and, in addition, one which appeared with a variable interstimulus onset at a visual angle of 8° on the left or right side of the screen. In the gap condition the fixation stimulus was faded out before the second stimulus appeared. Stimuli at each position (left, centre and right) were either critical (i.e. an open square) or non-critical (a closed square). This test, also known as the fixation offset effect paradigm, examines eye movement control at the level of the superior colliculus (Schiller et al., 1987; Forbes and Klein, 1996), but in the overlap condition it also entails a visual extinction condition. Our patient showed a distinct fixation offset effect for left-sided stimuli: in the overlap condition the patient did not perceive one single left-sided stimulus when either her right or her left eye was covered. In the gap condition she failed to notice 20% of the stimuli. In later investigations with this task she detected all of the stimuli in the gap situation, but still failed on the targets of the overlap condition (see Table 2). The control group (n ⫽ 8) missed no targets at all. We also used the TAP to investigate performance in a serial visual search task (Treisman and Gelade, 1980; Treisman and Sato, 1990). In this test we presented 25 squares in a 5⫻5 matrix. These squares were open at one of the sides or at the bottom. The subject was asked to search for a square which was open at the top. There were 100 trials; 50 included a square which was open at the top. For these 50 trials the critical squares were equally distributed over the 25 cells, so that a target appeared twice at each position of the matrix. The semi-random distribution of targets enabled an analysis of the search efficiency in the five columns. Several investigations have shown that neglect patients show a gradient of search efficiency, running from the left to the right in similar tasks (Eglin et al., 1989; Hildebrandt et al., 1999a). Our patient clearly found fewer squares on the left side, regardless of which eye was covered, but she hardly had any problems with critical stimuli on the right side (see Table 2). Most of our control subjects detected all critical targets and their performance did not differ for both hemi-fields (see Table 2). Extinction of acoustic and tactile stimuli was tested by standing behind the patient and producing two similar click sounds or by touching her shoulders. She had no problems determining the location of single and double tactile or acoustic stimuli. Follow-up The patient received neuropsychological training five times per week for 3 weeks using the software package VILAT (Hildebrandt et al., 1999b). After treatment she had regained a fair reading ability. This recovery was also confirmed in formal testing. Three weeks after the first investigation, she failed in only 50% of left-sided critical targets in the eye movement test in the overlap condition. In line with this finding, she reported that her vision had improved. Discussion Our patient suffered from a bleeding into the caudal and medial part of the cerebellum and into the brain stem (see the dysarthria and the abducens paresis), caused by a ruptured aneurysm of the PICA, and leading to a left-sided hemi-inattention as demonstrated by several clinical and experimental tests. A first explanation for this impairment could be that the lesion disrupted a corticocerebellar network, which interacts via the frontopontine tract (Schwarz and Thier, 1999; Schmahmann, 2001a). The significance of the cerebellum as a nodal point of this network for cognitive tasks has recently become a topic of intensive research and discussion (Akshoomoff and Courchesne, 1992; Daum and Ackermann, 1995; Schmahmann, 2001b). Numerous positron emission tomography and functional magnetic resonance imaging studies, as summarized by Desmond (2001), have shown that the cerebellum becomes activated during working memory tasks, and that this activation mirrors the laterality of working memory functions in the pre-frontal cortex. Our Visuospatial hemi-inattention 327 Table 2. Investigation of visuospatial attention Covert shift of attention Target left/arrow left Target right/arrow left Target left/arrow right Target right/arrow right Patient Control group 875 ms 249 ms 533 ms 289 ms 1230 ms 273 ms 482 ms 249 ms Left Centre Right 1632 ms Omissions: 2/10 – Omissions: 10/10 1028 ms Omissions: 0/10 – Omissions: 10/10 550 ms Omissions: 0/10 628 ms Omissions: 0/10 856 ms Omissions: 1/10 1349 ms Omissions: 7/10 915 ms Omissions: 1/10 907 ms Omissions: 3/10 503 ms Omissions: 0/10 592 ms Omissions: 0/10 543 ms Omissions: 0/10 577 ms Omissions: 0/10 536 ms Omissions: 0/10 556 ms Omissions: 0/10 524 ms Omissions: 0/10 589 ms Omissions: 0/10 Binocular Fixation offset paradigm Patient Left eye only Gap Overlap Right eye only Gap Overlap Control group Gap Overlap Serial search Column 1 (left margin) Column 2 (centre left) Column 3 (centre) Column 4 (centre right) Column 5 (right margin) Left eye only 6316 ms Omissions: 5/10 (50%) 5236 ms Omissions: 4/10 (40%) 2392 ms Omissions: 7.5% 7092 ms Omissions: 5/10 (50%) 7360 ms Omissions: 7/10 (70%) 2398 ms Omissions: 8.75% 6786 ms Omissions: 4/10 (40%) 6714 ms Omissions: 4/10 (40%) 2492 ms Omissions: 6.25% 5456 ms Omissions: 0/10 (0%) 5181 ms Omissions: 1/10 (10%) 2669 ms Omissions: 8.75% 5145 ms Omissions: 0/10 (0%) 5393 ms Omissions: 0/10 (0%) 2429 ms Omissions: 12.5% Right eye only Control group patient’s impaired performance on the verbal two back paradigm corresponds with these results, because in functional brain imaging such a task leads to a common activation of the left prefrontal cortex and the right cerebellum (Braver et al., 1997; Callicott et al., 1999). On the other hand, the evidence for visuospatial attention deficits after cerebellar lesions is not as clear as for working memory functions (Daum et al., 2001; Justus and Ivry, 2001). Although there are several functional brain imaging studies showing a cerebellar activation during visuospatial shifts of attention, the authors of these studies are cautious in interpreting these results (Akshoomoff and Courchesne, 1994; Nobre et al., 1997, 2000; Kim et al., 1999). So far, the clinical reports have focused more on specific experimental measures than on overt symptoms (i.e. difference in effective cue intervals between cerebellar patients and healthy subjects; Akshoomoff and Courchesne, 1992; Townsend et al., 1999). Recently, Silveri et al. (2001) published an investigation on a patient with a right cerebellar lesion developing a rightsided neglect. This report clearly argues for a contribution of the cerebellum to visuospatial attention. But, the ipsilesional inattention of their patient and the fact that the critical fibres, connecting the cerebellum with the parietal and the frontal lobes, cross at the level of the Ruber nucleus discard a similar interpretation for our patient. Her bleeding involved the right cerebellum and not the left. The right cerebellum interacts with different left-hemisphere cortical areas. If an interruption of this network were the reason for the observed impairment, one would expect a right-sided inattention [note, however, that irrespective of the target side, a higher activation of the right cerebellum is reported by Nobre et al. (1997, 2000) from functional brain imaging in visuospatial attention tasks]. A second and more plausible explanation is therefore that the bleeding unilaterally interrupted the central tegmental tract which originates from the noradrenergic A1 and A2 neurones. This ventral noradrenergic fasciculus converges at the level of the locus coeruleus with the dorsal fasciculus and then innervates as a part of the reticular activation system different ipsilateral regions of the cerebrum (Nieuwenhuys et al., 1991). Recent investigations have shown that the activation system interacts closely with the cortical visuospatial attention system (Posner, 1993) and that a higher level of activation also brings about an attenuation of neglect (Robertson et al., 1998). Animal experiments have given evidence of hemi-inattention following unilateral lesions of the dopamine system at the level of the substantia nigra (Apicella et al., 1991; Annett et al., 1992). The close correlation between the phasic alertness system and the visuospatial attention system in the right hemisphere (Paus et al., 1997; Sturm et al., 1999) and the significance of noradrenalin for this system (Coull et al., 1999) suggest that interruptions somewhere in this system may result in symptoms which are functionally very similar. This neuroanatomical explanation also accords with specific features of our patient’s functional impairments. First, in contrast to neglect patients, she was always aware of her disorder. Neglect patients rarely show such an insight into the disturbance (‘anosognosia’; Babinski, 1918). This 328 H. Hildebrandt, K. Spang and M. Ebke may be a consequence of, in addition to hemi-inattention, an impaired ability to represent the spatial layout of the environment, as repeatedly pointed out by Bisiach (Bisiach and Luzzatti, 1978; Bisiach and Berti, 1989). Therefore, neglect patients might not have the possibility of evaluating a mismatch between the expected and the perceived spatial environment. Actually, our patient did not show any kind of representational deficit, as she solved the block design test and had no problems with drawing a clock, tasks which both presuppose an internal representation of environmental space. Second, the impairment in complex motion perception (compared with simple motion perception) and in the neglect test of the TAP (compared with perimetry), argue for an attentional basis of our patient’s deficits. This is supported by the fixation offset experiment and the serial search task where the most striking impairment was revealed. Both tasks involve extinction or controlled processing. Third, the relatively fast recovery also argues for a deficit of attention, and not of essential visuospatial processes. Fourth, attention testing revealed a marked reduction of alertness. 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Received on 15 February, 2001; resubmitted on 16 July, 2001; accepted on 14 January, 2002 Visuospatial hemi-inattention following cerebellar/brain stem bleeding H. Hildebrandt, K. Spang and M. Ebke Abstract Neglect is a unilateral lack of responsiveness to stimuli caused by visuospatial hemi-inattention, a unilateral representation deficit and/or a unilateral hypokinesia. It results most frequently from right-hemisphere brain damage, particularly of the parietal lobe but also of the frontal cortex, the basal ganglia, the thalamus, and recently it has also been described after a cerebellar lesion. We report a patient with right-sided bleeding of the posterior inferior cerebellar artery, who developed a left-sided visual hemi-inattention. She had no visual field defects, yet she had problems detecting left-sided targets in visual extinction. Furthermore, she was impaired in detecting complex motion on the left side and targets in a fixation offset paradigm. Reactions to left-sided targets in covert shifts of attention were slowed in the invalid condition. Her text reading was impaired as she could not always find the initial word of the next line. However, she was aware of her deficit. Her visuoconstructive ability was normal and she gave no indication of tactile or acoustic extinction. As the cerebellar lesion was located in the right hemisphere and the inattention involved the left side of space, we suggest that the damage to the right brain stem led to a transient imbalance of the noradrenergic ascending activation system which may explain her hemi-inattention. Journal Neurocase 2002; 8: 323–9 Neurocase Reference Number: O265 Primary diagnosis of interest Basilar aneurysm bleeding affecting brain stem and cerebellum Key words: visuospatial hemi-inattention; visual search; visual extinction; movement perception; brain stem; cerebellum Scan, EEG and related measures Structural magnetic resonance imaging, VEP, P3 Standardized assessment Neuropsychological examination, reading time, extinction, conjunction search, target detection in a gap and an overlap condition, Posner paradigm, movement perception, line bisection, clock drawing Other assessment Neurological investigation, visual fields (twin fields) Lesion location d Right basal cerebellar hemisphere, brain stem Lesion type Basilar aneurysm bleeding Language English