Article of Interest: Academic Chapter Examines the Use of Neuroscience Evidence in Brain Injury Cases Across 6 Countries

In Professor Denno’s own study, she exam­ined the cas­es of 7,776 defen­dants — near­ly half of whom faced the death penal­ty — involv­ing brain injuries from 1900 – 2020 and shared four key find­ings. First, 7.73% of cas­es raised infor­ma­tion about a defendant’s brain injury, per­haps due to the impor­tance of oth­er fac­tors in the individual’s case. Second, cas­es with men­tion of brain injury increased over time from 4 – 5% dur­ing 1900 – 1980 to 14% in 2020. Third, there was no dif­fer­ence in the state’s argu­ment of future dan­ger­ous­ness when com­par­ing brain injury cas­es and non-brain injury cas­es; in fact, a claim of future dan­ger­ous­ness relat­ed to neu­ro­science evi­dence only occurred 4% of the time. And final­ly, of the cas­es in which a future dan­ger­ous­ness issue was raised in brain injury cas­es (26), 65% of cas­es explic­it­ly relat­ed the risk to a defen­dants’ brain injury, where­as 35% asso­ci­at­ed the future risk with anoth­er neu­ro­sci­en­tif­ic con­di­tion the defen­dant had, not with their brain injury. 

While Professor Denno did not find a dou­ble-edged sword effect in her study, she notes that this lack of find­ing does not con­firm the absence of such an effect, pro­vid­ing two cap­i­tal case exam­ples to illus­trate the poten­tial work­ings of such an effect in the U.S. crim­i­nal legal sys­tem. Professor Denno notes that in People v. Buss the pros­e­cu­tion high­light­ed the ​“intractabil­i­ty of a defendant’s brain injury,” where­as this same argu­ment was found to be unsuc­cess­ful in United States v. Runyon. While the pros­e­cu­tion tried to argue that evi­dence of Mr. Runyon’s brain injury was ​“weak” and ​“dou­ble-edged,” the U.S. Court of Appeal for the Fourth Circuit reversed the low­er court’s dis­missal of the inef­fec­tive assis­tance of coun­sel claim, agree­ing that defense coun­sel should have intro­duced key evi­dence of brain injury as a mit­i­ga­tor. In gen­er­al, Professor Denno explains that U.S. courts have con­sis­tent­ly found that exam­in­ing defendant’s ​“cog­ni­tive or intel­lec­tu­al defi­cien­cies” is a key part of mit­i­ga­tion, par­tic­u­lar­ly in cap­i­tal cas­es. Although the devel­op­ment and pre­sen­ta­tion of mit­i­ga­tion is a pri­or­i­ty, Professor Denno notes that the poten­tial reha­bil­i­ta­tion of a defen­dant is ​“far less, if ever, a fac­tor with respect to neu­ro­sci­en­tif­ic evi­dence because the death penal­ty or the prospect of a harsh sen­tence looms.” She explains that ​“reha­bil­i­ta­tion is not con­sid­ered rel­e­vant in the way it could be in non-death penal­ty coun­tries where sen­tences are far less severe.” 

Although the inter­na­tion­al stud­ies var­ied method­olog­i­cal­ly (e.g., types of crimes, times­pan), they all relied on data from legal data­bas­es to inves­ti­gate the use of neu­ro­sci­en­tif­ic evi­dence, such as neu­roimag­ing tests (e.g., MRI), non-neu­roimag­ing tests (e.g.,psy­cho­me­t­ric tests), and expert tes­ti­mo­ny in crim­i­nal cas­es. Professor Denno found there to be a con­tin­u­um for a dou­ble-edged sword effect, with Slovenia on one end and England and Wales on the oth­er. Slovenia was an out­lier in hav­ing no dou­ble-edged sword effect; there was an empha­sis on mit­i­ga­tion and reha­bil­i­ta­tion in their crim­i­nal legal sys­tem, with this reflect­ed in alter­na­tive treat­ment options. Although two Australian stud­ies found a dou­ble-edged sword effect, the 2023 study focus­ing on sen­tenc­ing cas­es found that neu­ro­sci­en­tif­ic evi­dence more like­ly led to lenien­cy in cas­es (85%). The Netherlands study not­ed the pres­ence of a dou­ble-edged sword effect par­tic­u­lar­ly in brain injury cas­es with a high risk of severe vio­lence, but sen­tenc­ing mit­i­ga­tion was still pos­si­ble due to their crim­i­nal legal system’s empha­sis on pro­vid­ing defen­dants oppor­tu­ni­ties to improve. The Canadian study found a dou­ble-edged sword effect, espe­cial­ly giv­en the pre­sumed per­ma­nen­cy of brain injuries and the lack of appro­pri­ate treat­ment alter­na­tives in the sys­tem. Although the England and Wales study did not explic­it­ly address the dou­ble-edged sword effect, the study explains how the pros­e­cu­tion and defense both use neu­ro­science evi­dence; Professor Denno found them to fall on the fur­thest extreme of the con­tin­u­um, as the pros­e­cu­tion is more like­ly than the defense to intro­duce neu­ro­sci­en­tif­ic evi­dence and both nation’s sys­tems have lim­it­ed reha­bil­i­ta­tion options. ​“This chapter’s stud­ies show that the risk of the dou­ble-edged sword effect is too low for defense attor­neys to jus­ti­fy with­hold­ing neu­ro­sci­en­tif­ic evi­dence con­cern­ing a defendant’s brain injury, even when the injury appears to be per­ma­nent or untreat­able,” con­clud­ed Professor Denno.